Mach3, Vcarve Pro.
I was using a pocketing routine and it ran through the Gcode perfectly cutting four levels of 0.100" at each depth on three pieces.
When I started the fourth piece it cut to -0.300" just fine but when the Z was to move to the -0.400" level it didn't stop going down until I hit the E Stop button.
On looking around I saw that the display read -0.400" and the Z was probably at the -0.600 level.

This has happened a couple of times before (holes in the table as proof, LOL), but I failed to notice the display reading so I cant say what was displayed

Any ideas as to what happened?

Thanks