Yes, it's the result of the UI matrix rendering changes (I hope you now enjoy better frame rates with it...).
I forgot to remove lines that are no more needed. In indra/newview/llmediactrl.cpp, around line 720, change to read:
(the change is the #if 0 ... #endif clause).
Then recompile the viewer, and things should be back in order. This fix will be part of next releases.