ImageField Thumbnail does not appear|missing for images having an exact size of 100x100.

This is due to the image_scale function called.
Since it will not scale an image to a new one with the same size.

Added is a patched code for the imagefield_file.inc file.
Which changes the eval in the imagefield_file_insert function,
to also check for same size.

One could also create thumbs using the imageapi if available.
If so create the thumb using the imageapi_image_scale
function with an $upscale = true for images which need to be upscaled.
Then all thumbs woul have same size.