Grounding the Heater Core

[Txoof]

I came across this post urging the grounding of the heater core:
http://wiki.makerbot.com/forum/t-325073

According to the post, it's possible to fry the extruder controller if
the heater core fails. The solution provided to prevent scorching the
board is to run a grounding cable from the extruder plate down to the
body of the PSU.

I followed the suggestion and hooked up a solderless lug; upon pulling
the plate down to ground, the thermometer reading shot down to zero.
At first I thought the thermometer had broken through the kapton tape
insulation. I removed the thermometer completely from the extruder
and then pulled the plate to ground again with the same result.

1) Is grounding the extruder really necessary?
2) What could possibly be causing this strangeness?