I dont know the answer directly but knowing your installation as I do, I wonder if it's something to do with the Cloned Incident domain you have.
There used to be a problem running MDM with cloned domains, and I remember I had to run a SQL script before upgrading, but didnt think that was needed post 7.3.
Just a thought and I might be off base.
Hi Lianne, I fear Julilan is correct. I am aware of there being some issues with running the MDM against cloned domains. I suggest you log this formally with support. Andy
Fixed - had a statistic on the lc_action_value table that reference the lc_value column - scripted the statistic, then dropped it, ran MDM then reapplied it