Applying an adjustment layer / or adjustment TO a layer in a grayscale image is NOT happening!

Question

I'm a long time user of Photoshop, but must admit to being stumped here. I have a very high resolution scanned image from a B&W antique engraving, and I'm trying to "open up" some of the lines to bring out the details in the engraved image while keeping the image as close to the "line art" B&W of the original as possible.
I have the image now "cleaned up," having taken out the yellow color casts, etc., and have a grayscale 8-Bit image in the Photoshop file.
I've discovered that I can use an adjustment TO the layer itself, or an adjustment layer on the layer in the grayscale image to take away some of the density and "open up" the line art a little, so it has better details by effectively "choking" the dark lines back to make them less thick and dense.
Here's the thing, though: 
When I tried making the adjustments via image > adjustments > levels DIRECTLY ON the layer (instead of using and adjustment layer to achieve this), every time I hit the OK button to accept the adjustments I've made that way, the dialog box closes and the layer seems to revert to looking just the same as it did BEFORE I opened the dialog box to adjust the layer!
When I try making the adjustments by using an adjustment LAYER, and I try to save the Photoshop image as a TIFF file, I find that when I open the saved TIFF image, the layer adjustment I'm seeing in the source Photoshop file has NOT been applied, and the image in the saved TIFF file looks just as dense as the original, unadjusted image in the Photoshop file!
What am I doing wrong here?  I want to be able to save out that adjusted image as a TIFF file to use in designs, but I cannot seem to save it as a TIFF that actually CONTAINS or reflects these adjustments after having MADE the adjustments! 
Whazzup?!!

Answer 1

Well, I took the layered TIFF file you gave to me and opened it in Photoshop, reviewed the adjustment layer in there and its effect -- thanks: you get what I was trying to do -- and then saved it out as a flat TIFF image, and when I reopened it, voila!  it looked like the adjustment had indeed been applied.  So this IS a real head-scratcher indeed.
I've now tried going back to my source file and doing the same thing.  One thing that I notice is that when I do the Save As of the TIFF with the adjustment layer in it (OR the PSD file, for that matter), when I go to Save YOUR file, the Layer Compression Options are grayed out, but when I go to Save MY file, the Layer Compression Options are active.  I've tried now saving both with RLE layer compression AND As a Copy ("discard layers and save a copy"), and neither works.
I noticed, too, that your file had the layer below the adjustment layer still as a "Background," instead of a named layer, so I went back and applied an adjustment layer to a copy of my TIFF file, leaving the image in its layer as a Background layer, and still this did not work.
The only other difference I saw between your TIFF file and mine, is that mine contained transparency, as I've silhouetted away a portion of the image to isolate the central image of the scanned engraving. But even when transparency is not a factor (i.e. I go back and start with a flattened, nontransparent image layer of my TIFF file with a single Background Layer, and I apply the adjustment layer to that, I get the compression options grayed out on Save, and STILL the saved TIFF image I get out of it has "reverted" to the unadjusted appearance.