I have 3 machines, one of which runs Mach 4 (avid) and the other two (blue elephants) running mach 3. I have a marker operation on these machines that I drag sharpies across the material to draw on them. Occasionally they start to fade during the operation. If I hit FEED HOLD and change the marker, the Mach 4 machine simply continues the path. The other 2 Mach 3 machines will start the forward motion but raise the z axis at the same time until it rises about 1.94".  Any ideas as to what set this function? Is it controller, Mach settings?  I run the same Gcode for all machines.  I have to "run from here" on these machines where as just hit start again on the avid Mach 4. 

It could be possible its a safe Z setting. Goto Config/Safe Z setup and see if there is something there to adjust.