Hello,
I have the problem that ZBrush is frequently crashing when I hit a button to perform a more cpu intense task like decimation master, unwrapping, or sometimes even at a simple mirror object. Not always of course but I would say in 20% of the cases. Is this a known problem and is there a possible workaround? I’ve tried turning off the cpu multidraw, that makes my fans go crazy sometimes. But it both cases it’s happening 
My specs:
OSX Yosemite (newest version)
12GB RAM
2.6 Intel Quadcore