Yes, I'd definitely consider that a bug, though it might be considered a borderline FR as the mobi code is all reverse engineered. Regardless if you post these details and your test case to the
bug tracker I would expect it to be addressed.
Don't know what the reason with Imageshack is precisely, but I regularly travel around the world and see the frog/error wherever I go, so IP address wouldn't be the reason. I assume if I have the problem then other users must too, but maybe it's not so common.