The following steps are crashing Zbrush 4R6 reliably:
- Draw a ZSphere
- Enable Edit Mode
- Enable EditSketch
- Draw ZSketch geometry
- Disable EditSketch
- Enable ShowSketch
- Disable Edit Mode
- Clear canvas (transparent ZSketch remains on canvas)
- Click and drag on canvas
- CRASH
2010 27" iMac 2.93 GHZ i7, 16 GB RAM. OS X 10.7.5