Hi Trev,
As Stuart said, it's probably the culprit.
Polarising filters certainly are good at reducing reflections from
dust in the air, so from a non-technical view point it could
follow that most of the relection light from the Witches Head is
polarised light.
It would be a good comparison to try and exactly duplicate your
first night with a second non filtered attempt, same processing
routine etc....to demonstrate just how 'polarised' the light from
the WH really is....if that's what caused it.
One thing buggers all this theory up though for me....why did the
Running Man and parts of M42 show up so well?
Just purely a much brighter reflection neb, or another reason?
Steve