Dean,
My tests were with a simple part.
Your work around is painful and should not be necessary.
Can you upload you part and give the exact version and cut of s/w?
Did you confirm that the material had not changed by right click > edit definition on the material assignment in the model tree?
How did you determine that the material had not changed? Was this by reviewing displacements, stresses?
('correct' is via a green star just beneath the last line of a reply I think and yes it is up to you as far as I know. Your question isn't answered yet ! )