Layers disappear in Windows XP thumbnail view

[mingo33]

When I save a PSD as a JPG I thought the layers got merged and the JPG did not contain layers but when I store the JPGs in a folder on WinXP and then turn on thumbnail view the layers disappear and I can see the original photo without layers in the thumbnail preview. If I open the photo in WindowsXP picture viewer the layers return and they are still there. Why is that?

[NEMESIS]

I didn't quite understood this. Could you please post a screenshot of that? Please don't use more then 800px wide image in forums because it will overflow the boundaries of the website.

[mingo33]

Thanks for the response. Basically I have taken a photo and added a solid shape to the photo to obscure some details. It looks fine when I open the photograph in XP photo viewer but if I turn on the thumbnails preview option in the windows XP folder where the photo is stored then the thumbnail is missing the shape and you can see all the details (although obviously they are quite small in the thumbnail). I can't really post it as the reason for adding the shape is to obscure details for web publishing. Any ideas why that would happen? I will see if I can reproduce the effect on another photo.

[mingo33]

^Correction - the edits were done in MS Paint not photoshop. It is quite easy to reproduce. Open a JPG photo in MS Paint. Add a solid shape to the photo. Save it. In Windows XP file explorer turn on thumbnails view. You can see a preview of the modified photo but the added shape is missing. Is the original thumbnail cached from before the edit or does the JPG contains layers which get stripped during thumbnail generation?

.....
edit:-
Actually - the answer may be here

http://www.sentex.net/~mwandel/jhead/

looks like the Exif wrapper around the JPG files contains a cached thumbnail

[Scaffomoffife]

In a recent thread Sergey suggested to a user "...to use "View as" type "Custom" to display a thumbnail and link it to the View page. ". Would anyone happen to have an example of code required to make this possible?
Thanks

[NEMESIS]

When adding the shape after flatten your artwork so it becomes a single layer document. Save as JPEG i bet it will work. Then if you need to change the EXIF data there is program called EXIFER. It may do some good for you.