I think there should be a sleep of maybe 100ms after setting the new vref and tempscaler in the function setTempRange() in the file GenericExtruder.java.
without sleep it could happen that the software gets the old temperature measurement from the pic again and increments or decrements the values again.
this is more likely if only the extruder-board is connected.
andi
PS: is this forum the right place to discuss such thinks, or exists there a better place?