More information on this...
Note that this was initially failing on composition. It was not giving the field access exception that in retrospect it should have given.
Apparently it is touching the implementation that fulfills IUser more than I expected. It is discovering at this point, not later when the instance is actually created, that there is an issue (another field access exception as I was actually exploring field
access exceptions for an article) with the implementation of IUser. Not IUser, but the implementation. It would appear that it tried to fulfill those imports as it created the PartCreator.
Is this how it is supposed to work?
Could I request that the MEF team consider the ability to turn off or otherwise control stable composition in a future version of MEF? It's good for most apps some of the time, some apps all the time, and some apps none of the time.
I still want to understand this, but I have it working I think