With this version of an iPhone app, I'm trying to create a new core data model version in which I'm taking two existing entities and changing them to inherit from a brand new abstract entity. I'm also trying to move several of the shared properties from these entities onto the new abstract entity.

When I run on an existing version of the app I get a NSInternalInconsistencyException 

Cannot merge multiple root entity source tables into one destination entity root table

Up until this version of the app I've gotten away with "lightweight" migration. Does this exception mean that I'll need to create a Mapping Model?

iphone ios cocoa core-data migration
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