Yes, the issue with Ubuntu 13.04 has been brought to my attention, in another thread here. viewtopic.php?f=7&t=143 It looks like all the coordinates have been clipped to integers when they should be floating point values... weird. I had some discussion with that guy via email, and he said everything was fine until he upgraded from 12.04 to 13.04 recently. Was that the situation with you too?
He also said the same problem occurred in virtualbox as well, and with both 32 and 64 bit binaries. I installed 13.04 myself to check, but I could not reproduce the problem on my computer with either 32 or 64 bit binaries. Kinda stuck about what to do next. It seems like it is behaving differently on different PCs, with the same OS and binaries... is that even a possibility?
Unfortunatelly I have not run the app on other versions of ubuntu than 13.04 32-bit. Current ubuntu on my laptop is clean install. As a suggestion: try to install all currently available updates and reboot.
Now I'm using windows version through wine, it works well.