Re: Weird behavior and crashes...
Can you post a screen shot of your parameters? Step-over, step-down etc. Also, can you attach the tool? It will have a .ctr extension, and most likely will be found in C:\Programdata\5XCNC\MadCAM\5.0\Cutters. If it's not there, then you most likely have your own custom place for it (as do I). I'm asking for this because I (and much of the rest of the world) work in metric so having the actual tool you used will be beneficial.
FYI... I changed the units to millimeters in Rhino, let Rhino scale the model up 25.4, and tried with my Ø4mm endmill (Ø.157"). I didn't see any problems. It worked well. I think to truly test what you are seeing, I need to do it in inches with your tool and parameters.
Thanks,
Dan
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)