Hello,
What did you configure for the Z homing in the plugin config?
If the Axis is set to use a "Home Sensor", then it should back off the home switch to the point where it gets deactivated. Perhaps the Homing setting was set to "Use Index Pulse Only"?
There is also the off chance that the sensor may be experiencing some noise which causes the Motion Controller to read the signal as deactivated when it shouldn't be. You can try going to "Config->General Config". On this window, look to the upper right corner for the "Debounce Interval" setting and set this to something like 10-50 (this value is in milliseconds even though the window says "x40 us"). This setting controls the debounce for the digital inputs in order to filter out some noise.
-Marc
Vital System Inc.