I would wager that your gpu is artifact sending garbage to you xserver which is being captured by your screen shot software. Then again I would be wrong.
I notice that your issue is real similar to this :: Moving and vanishing lines of code; trouble with Eclipse's XML Editor Where I noticed "The reason you get weird visual artifacts is that if a file contains broken DOS line endings (multiple carriage returns without a newline for each carriage return)"
Now I don't know if you can get teh android team to port their solution up onto a mac but that leaves me with the question, does Select All, Copy, Paste resolve the glitch?