[Bug] GR doesn't display a thumbnail for random JPG files, and crashes on upload if attempt to upload anyway

This is a very weird bug that I've had every since I used GR for the first time (I'm currently using 1.5.1 b36 on XP SP2).
At first I thought it was the files that were causing this, but on a wide range of images, old and recent and straight out of the camera, I still get a few pictures which GR refuses to show before upload (the thumbnail list).

Every other pictures are fine, displaying a thumbnail, and they upload correctly, but for theses files :
- no thumbnail display prior to upload
- upload crashes (or rather gets stuck on a loop) when it gets to them

It doesn't depend on filesize (I've uploaded 9mb pics fine, and it happens also on 300kb files) and it's not specific to one batch of JPG files. I've used files from a wide range of different sources, and I still always get a few problematic ones all the time.

This is especially annoying since GR stops entirely on a bug like this, meaning a whole batch upload gets stuck and works only after cancellation and deletion of said problematic files.
GR should at least stop trying to upload after a few seconds and signal that the files couldn't be uploaded.
But eventually, I'd like to know why this happens so randomly.

Too bad since it's a really great software in every other area.
Thanks.