My GIMP suddenly won't do transparencies of any kind, most notably, it has recently taken away my ability to paste any image that has transparency in it, it simply fills in the space with horrendous black. GIMP, you dun goof'd. What do?
Is it only when you save that it does that? Or is it just all the time? I think if is the same as Photoshop in this way, then if the colors aren't in 8 bit you can find them when you are altering image size, if its not there, I don't know where it'd be. Sorry, not too familiar with Gimp. I would just make sure its on 8-bit, is saving as .png files if you want transparency after its saved... My thoughts are its trying to make everything .jpg files so it adds a black matte to everything but I probably am wrong.
Save your files in .xcf format, and delete the program. Re-download it. Most efficient way to do it. Photoshop crashes, so can GIMP. My guess is the coding gets screwed up because of so much awesome is created. So re-downloading it should fix the problem.
And if that crashes? Oh yea. That's about $800 to replace. Haha. Much more reliable solution, isn't it?