Neikius: edit: Actually upon reading what you said the second time I think you meant the unofficial opensource driver patches/branches? I am definitely using the default ubuntu things and this is actually the only problem I can think of that is seriously broken on the "radeon" open source driver.
Oh and I hope you don't mean that I should use the fglrx driver, since I've really had bad experience using that. Only the fps is sometimes a tad higher, everything else is much much worse than the opensource driver...
And thanks for the reply, I've managed to make the game run using wine though and I guess that will have to do. I can confirm game works on nvidia binary driver + kubuntu 14.04 just fine.
We just put out version 1.52 for all three operating systems. Perhaps this update will help you run the game in Linux now without using Wine? :)