Oh, OH! I see what's going on here. Yeah it's annoying, but a pretty easy fix.
Judging from the GPU you have it's safe to guess you also have an early Intel i series CPU, which is where the problem lays.. Partially.
If you prod the AMD catalyst thingy you'll find (somewhere) an option relating to power saving and which GPU it should use. Tell it to always use the "high power GPU" or whatever they have it listed as now, also make a custom setting thingy for Toribash and also tell it to use the AMD GPU.
See the thing is GL stuff tends to get ignored unless it's Quake or a 3D rendering tool effergy, and AMD's all "yo fuck this shit" and uses the crappy GPU built into the processor thinking it's doing the right thing blah blah. So yeah, with a bit of prodding setting you'll not only fix the 'bug', you'll also improve the frame rate and other exciting stuff like that.