Sometimes I have your problem. What I do is just press back and reload. If it doesn't work I do it a few more times and it usually works then. It's a bother I agree.
If that doesn't work, close and reopen your browser?
Edit: it's definitely not your PC. I get it sometimes, it's server-side I think. What browser do you use?
Edit 2: didn't see the first post.
Seems like you have a dilemma in your hands! Have you tried saving the image and uploading it as a sigpic?