Jpeg lossless rotation in organizer?

Question

Currently using PSE 4, but moving up to 7 soon.  I've read in previous threads that within the Organizer jpeg rotation is lossless, however I've observed that after doing an initial set of rotations there is a decrease in file size*; subsequent rotations however, do not change the file size. Does anyone have an explanation for this observation, and is the rotation not lossless afterall?  (*For purposes of viewing vertically oriented images correctly in Windows XP and Vista, I've found that I need to rotate the images horizontally and then back vertically, otherwise they remain oriented horizontally when viewed outside Elements.  This is problematic when burning images on CD/DVD to share with others.)  Thanks.
Ethan

Answer 1

Also, I looked in Edit>Preferences>Files, as well as elsewhere in PSE4, and found no information or option for rotation using orientation metadata.
I no longer have PSE 4 installed. But the options may be called Edit > Preferences > Files >Fast JPEG Rotation and Fast TIFF Rotation -- ignore any description you may find in the PSE 4 User Guide, since based on what I see in the PSE 5 Guide, it's completely garbled.  (The names of the options and their descriptions got fixed by PSE 7.)
In PSE7, if the option were unchecked, I'm assuming all vertically oriented images would come in horizontally, and thus require rotation anyway.  If this is so, I'm not sure what's gained by unchecking the option?
When you take a vertically oriented photo with many newer cameras, the camera records the actual JPEG image horitontally oriented, and it records in the file's metadata the following setting:
Orientation: Rotate 90 CW
In general, when you import a photo into PSE 7, it always obeys the setting of the Orientation field, regardless of the setting of Rotate JPEGs Using Orientation Metadata. So when you import that vertically oriented image into PSE 7, it will come in correctly oriented, vertically.
If you then export that photo and view it in a non-conforming application, the photo will appear horizontally oriented, because that's how the actual image is recorded in the file and because the application ignores the Orientation field.
If you uncheck the option and then rotate counter-clockwise, PSE changes the orientation field to:
Orientation: Horizontal (normal)
and it leaves the actual JPEG image untouched, since it is already horitontally oriented.  If you then rotate clockwise, PSE leaves the orientation field as:
Orientation: Horizontal (normal)
and it rotates the actual JPEG image to vertical orientation.  When you export that version to non-conforming applications, they will see the image vertically oriented.
When experimenting with this, be aware that at least some downloaders (e.g. the Windows Live Photo Gallery downloader) will read the Orientation field in a photo and rotate the actual JPEG image accordingly (depending on the options you've set).  They do this precisely because not all apps conform to the industry standard for the Orientation field.