We've known for a while that grid fields get lost when you have to add fields to Business Objects, but it seems now that all related assignment activity entries are lost too. There is no warning, no warning on deployment, and there is no way to tell what was there, either, unlike grids.
version 9.0.0.1432
More here:
http://metastorm.processmapping.com.au/post?id=4839694