Why won't Photoshop revert to earlier history state after image resize when scripted?

Question

I've written an Applescript to automate watermarking and resizing images for my company. Everything generally works fine —　the script saves the initial history state to a variable, resizes the image, adds the appropriate watermark, saves off a jpeg, then reverts to the initial history state for another resize and watermark loop.
The problem is when I try not to use a watermark and only resize by setting the variable `wmColor` to `"None"` or `"None for all"`. It seems that after resizing and saving off a jpeg, Photoshop doesn't like it when I try to revert to the initial history state. This is super annoying, since clearly a resize should count as a history step, and I don't want to rewrite the script to implement multiple open/close operations on the original file. Does anyone know what might be going on? This is the line that's generating the problem (it's in both the doBig and doSmall methods, and throws an error every time I ask it just to do an image resize and change current history state):
                    set current history state of current document to initialState
and here's the whole script:
property type_list : {"JPEG", "TIFF", "PNGf", "8BPS", "BMPf", "GIFf", "PDF ", "PICT"}
property extension_list : {"jpg", "jpeg", "tif", "tiff", "png", "psd", "bmp", "gif", "jp2", "pdf", "pict", "pct", "sgi", "tga"}
property typeIDs_list : {"public.jpeg", "public.tiff", "public.png", "com.adobe.photoshop-image", "com.microsoft.bmp", "com.compuserve.gif", "public.jpeg-2000", "com.adobe.pdf", "com.apple.pict", "com.sgi.sgi-image", "com.truevision.tga-image"}
global myFolder
global wmYN
global wmColor
global nameUse
global rootName
global nameCount
property myFolder : ""
-- This droplet processes files dropped onto the applet
on open these_items
  -- FILTER THE DRAGGED-ON ITEMS BY CHECKING THEIR PROPERTIES AGAINST THE LISTS ABOVE
          set wmColor to null
          set nameCount to 0
          set nameUse to null
          if myFolder is not "" then
                    set myFolder to choose folder with prompt "Choose where to put your finished images" default location myFolder -- where you're going to store the jpgs
          else
                    set myFolder to choose folder with prompt "Choose where to put your finished images" default location (path to desktop)
          end if
          repeat with i from 1 to the count of these_items
                    set totalFiles to count of these_items
                    set this_item to item i of these_items
                    set the item_info to info for this_item without size
                    if folder of the item_info is true then
  process_folder(this_item)
                    else
                              try
                                        set this_extension to the name extension of item_info
                              on error
                                        set this_extension to ""
                              end try
                              try
                                        set this_filetype to the file type of item_info
                              on error
                                        set this_filetype to ""
                              end try
                              try
                                        set this_typeID to the type identifier of item_info
                              on error
                                        set this_typeID to ""
                              end try
                              if (folder of the item_info is false) and (alias of the item_info is false) and ((this_filetype is in the type_list) or (this_extension is in the extension_list) or (this_typeID is in typeIDs_list)) then
  -- THE ITEM IS AN IMAGE FILE AND CAN BE PROCESSED
  process_item(this_item)
                              end if
                    end if
          end repeat
end open
-- this sub-routine processes folders
on process_folder(this_folder)
          set these_items to list folder this_folder without invisibles
          repeat with i from 1 to the count of these_items
                    set this_item to alias ((this_folder as Unicode text) & (item i of these_items))
                    set the item_info to info for this_item without size
                    if folder of the item_info is true then
  process_folder(this_item)
                    else
                              try
                                        set this_extension to the name extension of item_info
                              on error
                                        set this_extension to ""
                              end try
                              try
                                        set this_filetype to the file type of item_info
                              on error
                                        set this_filetype to ""
                              end try
                              try
                                        set this_typeID to the type identifier of item_info
                              on error
                                        set this_typeID to ""
                              end try
                              if (folder of the item_info is false) and (alias of the item_info is false) and ((this_filetype is in the type_list) or (this_extension is in the extension_list) or (this_typeID is in typeIDs_list)) then
  -- THE ITEM IS AN IMAGE FILE AND CAN BE PROCESSED
  process_item(this_item)
                              end if
                    end if
          end repeat
end process_folder
-- this sub-routine processes files
on process_item(this_item)
          set this_image to this_item as text
          tell application id "com.adobe.photoshop"
                    set saveUnits to ruler units of settings
                    set display dialogs to never
  open file this_image
                    if wmColor is not in {"None for all", "White for all", "Black for all"} then
                              set wmColor to choose from list {"None", "None for all", "Black", "Black for all", "White", "White for all"} with prompt "What color should the watermark be?" default items "White for all" without multiple selections allowed and empty selection allowed
                    end if
                    if wmColor is false then
                              error number -128
                    end if
                    if nameUse is not "Just increment this for all" then
                              set nameBox to display dialog "What should I call these things?" default answer ("image") with title "Choose the name stem for your images" buttons {"Cancel", "Just increment this for all", "OK"} default button "Just increment this for all"
                              set nameUse to button returned of nameBox -- this will determine whether or not to increment stem names
                              set rootName to text returned of nameBox -- this will be the root part of all of your file names
                              set currentName to rootName
                    else
                              set nameCount to nameCount + 1
                              set currentName to rootName & (nameCount as text)
                    end if
                    set thisDocument to current document
                    set initialState to current history state of thisDocument
                    set ruler units of settings to pixel units
          end tell
  DoSmall(thisDocument, currentName, initialState)
  DoBig(thisDocument, currentName, initialState)
          tell application id "com.adobe.photoshop"
                    close thisDocument without saving
                    set ruler units of settings to saveUnits
          end tell
end process_item
to DoSmall(thisDocument, currentName, initialState)
          tell application id "com.adobe.photoshop"
                    set initWidth to width of thisDocument
                    if initWidth < 640 then
  resize image thisDocument width 640 resample method bicubic smoother
                    else if initWidth > 640 then
  resize image thisDocument width 640 resample method bicubic sharper
                    end if
                    set myHeight to height of thisDocument
                    set myWidth to width of thisDocument
                    if wmColor is in {"White", "White for all"} then
                              set wmFile to (path to resource "water_250_white.png" in bundle path to me) as text
                    else if wmColor is in {"Black", "Black for all"} then
                              set wmFile to (path to resource "water_250_black.png" in bundle path to me) as text
                    end if
                    if wmColor is not in {"None", "None for all"} then
  open file wmFile
                              set wmDocument to current document
                              set wmHeight to height of wmDocument
                              set wmWidth to width of wmDocument
  duplicate current layer of wmDocument to thisDocument
                              close wmDocument without saving
  translate current layer of thisDocument delta x (myWidth - wmWidth - 10) delta y (myHeight - wmHeight - 10)
                              set opacity of current layer of thisDocument to 20
                    end if
                    set myPath to (myFolder as text) & (currentName) & "_640"
                    set myOptions to {class:JPEG save options, embed color profile:false, quality:12}
  save thisDocument as JPEG in file myPath with options myOptions appending lowercase extension
                    set current history state of current document to initialState
          end tell
end DoSmall
to DoBig(thisDocument, currentName, initialState)
          tell application id "com.adobe.photoshop"
                    set initWidth to width of thisDocument
                    if initWidth < 1020 then
  resize image thisDocument width 1020 resample method bicubic smoother
                    else if initWidth > 1020 then
  resize image thisDocument width 1020 resample method bicubic sharper
                    end if
                    set myHeight to height of thisDocument
                    set myWidth to width of thisDocument
                    if wmColor is in {"White", "White for all"} then
                              set wmFile to (path to resource "water_400_white.png" in bundle path to me) as text
                    else if wmColor is in {"Black", "Black for all"} then
                              set wmFile to (path to resource "water_400_black.png" in bundle path to me) as text
                    end if
                    if wmColor is not in {"None", "None for all"} then
  open file wmFile
                              set wmDocument to current document
                              set wmHeight to height of wmDocument
                              set wmWidth to width of wmDocument
  duplicate current layer of wmDocument to thisDocument
                              close wmDocument without saving
  translate current layer of thisDocument delta x (myWidth - wmWidth - 16) delta y (myHeight - wmHeight - 16)
                              set opacity of current layer of thisDocument to 20
                    end if
                    set myPath to (myFolder as text) & (currentName) & "_1020"
                    set myOptions to {class:JPEG save options, embed color profile:false, quality:12}
  save thisDocument as JPEG in file myPath with options myOptions appending lowercase extension
                    set current history state of current document to initialState
          end tell
end DoBig

Answer 1

As many others here I use JavaScript so I can’t really help you with your problem.
But I’d like to point to »the lazy person’s out« – with many operations that result in creating a new file on disk I simply duplicate the image (and flatten in the same step) to minimize any chance of damaging the original file if the Script should not perform as expected.