Is this an ATC machine? If not, did you at some point set it as an ATC with the setup routine? C8 isn't what you want to use for Safe Z setting. Perhaps go back through the tool setup and reconfigure it (Tools/ShopBot setup) to make sure it's not set for ATC if it isn't an ATC.
Really though, if you have a Z prox, having the Z axis go to full height is a better choice, and then your safe z is set in your design software.
Scott
"It’s easier to fool everyone than it is to convince them they've been fooled" - Mark Twain