It does not happen here with your xml so it is hard to see how it is an issue with the xml, assuming that is you attached the correct xml?
As I said earlier I loaded the standard screenset as I dont have that one you are using. So the only things I can think that would cause your issue are the screenset, a plugin or a brain.
There is no way the Z axis should move at all just by pressing the Stop button, that suggests there is VB in that button on the screenset you are using or you have a brain or macropump doing something when that is seen.
Hood