it appears I've found a bullet-proof way to crash my ZBrush in 10 seconds. *hooray*
In case you want to see if you can reconstruct this behavior, the steps are:
1. Drop to Canvas
2. Drag out new instance of object in 2.5D mode
3. Move Object
4. Drop again
5. Drag out new instance
(7. If it didn't crash at this point, try switching to move mode, that's what does it for me if ZBrush happens to survive this far)
This is 4R7 (32 & 64 Bit) on a Win 8.1 Machine.
Anyone facing the same problem?