Kudos on good sleuthing!  I spent maybe 8 hours on the research including discussions with heavy hitters at regional sized firms, local CPE people who specialized in MA taxation, and of course other CPAs.  Each had a different answer to the question as do the big tax softwares like Lacerte who was not helpful at all with this issue.

Lacerte has it's limitations and the further away from TX you are the more obvious so workarounds are a regular piece of the puzzle.  I would force a US/MA difference so the tax comes out properly to your research.  If the net difference is zero does it really matter how you get there?  Lacerte is no help.