I have 2 pictures, Imagine0017.jpg and Imagine0018.jpg, made with a Nokia phone. I concatenated them and I saved the result as fietel_chic.jpg, with a software (PhotoFiltre under WINE) that asked me whether to preserve the EXIF info or not. I said yes ==> fietel_chic.jpg has now the same EXIF info as Imagine0017.jpg (which is correct) ==> fietel_chic.jpg has now THE SAME THUMBNAIL AS Imagine0017.jpg (which is a bug) Xubuntu 9.10 beta, Thunar 1.0.1
Created attachment 2569 First image
Created attachment 2570 Second image, inherits the thumbnail
Created attachment 2571 Spot the 2 identical thumbnails
`killall Thunar ; rm -rf ~/.cache/Thunar/' DOES NOT fix the bug!
Fix: save the file again, with GIMP, and without any EXIF info!
AFAIK, it's because of the jpeg thumbnailer, which will use the thumbnail contained in the EXIF data when it's available (and since your two pictures have the same EXIF info, they'll have the same thumbnail). This doesn't happen when the pixbuf thumbnailer is used (here it's fine because tumbler chose the pixbuf thumbnailer by default, but I'm not sure it will be the case on another system).
This is not a bug in tumbler. If your EXIF data is out of date, then it is a bug in whatever application caused that. (It is a bit problematic that the pixbuf thumbnailer plugin and the jpeg thumbnailer plugin race over who gets to create the thumbnail though. But that's a different issue.)
I correct myself: It is not a bug in tumbler, unless there is a simple way to check whether the EXIF data is still up to date by means of libjpeg. But I doubt that.