Usually drifting on all axis is caused by a loose ground between the burny and the drive amps ( the drive signal return ) however the Burny 10 should notice this and correct the drift. As your machine does this mostly on start up and shutdown, ie when the burny software is not checking its position, this may still be the case.
I think the real problem is that the drives are enabled all the time. When the emergency stop is pressed the drives should be off, also when the Burny is booting up the drives should be off so the drift is not apparent.
You should check the drive enable relay, maybe it is stuck.
Perhaps contact Kerf as it is one of their machines. K N D automation in Athlone could sort it out, he is an ex Kerf engineer.
Techserv Cutting » British Quality and Innovation