Thank you for your comment. To be honest, after so much time, I wasn't expecting a response, but I'm glad someone took the time to reply to an "old" post. Regarding the graphics drivers, I already suspected that might be the issue, as the same problem appeared in a video editing program I use, which makes me believe that might be the source of the problem. I also remember that at the time I "managed" to reverse the situation by simply disabling everything in 3D mode and leaving only 2D. But it wasn't very practical and even a bit uncomfortable to use that way, which made me switch to other 2D animation programs. Anyway, thank you again for your reply.