GUI causing big drop in framerate

[Maars]

Ok, not sure if this has been discussed already although I can't find it by flicking through browser searches nor threads..... while playing a near perfect 64bit ksp on my ubuntu OS i find that after pressing F2 and making the GUI disappear, my framerate comes back to not perfect but very "playable", while having the GUI "on"' I have a big reduction in framerate, almost to a stuttering level, or rather, a 32-bit fully modded windows level, in other words I lose up to 30% of my framerate and it C R A W L S. Would anyone have any ideas as to what on earth is going on?