I quite commonly create a default alias on my dimensions with the name Description.
It would seem though that TM1 Contributor does not like this as a name for the alias on a nominated workflow hierarchy.
I could not understand why my alias was not displaying in Contributor but upon using a different name for my alias on the workflow dimension, suddenly everything came right again.
My suspicion is that there is some MDX call within Contributor that becomes invalid for some reason.