The list isn't legally binding, and is riddled with errors. You may as well ignore it in 99% of cases.
I agree however I believe law enforcement would arrest you based on the MSP determinations and tell you to sort it out with the judge. Ideally a letter from the MSP addressing the MCX could help avoid being arrested in the first place.
Anyone been arrested for possessing something on "the list" yet?
Seen police stationed at the range to do gun checks?
http://mdsp.maryland.gov/Organization/Pages/CriminalInvestigationBureau/LicensingDivision/Firearms/FirearmSearch.aspx
Do you have a letter from the MSP re-classifying the MCX as a "copycat" weapon (allowing the muzzle break instillation to make the rifle MD legal) instead of what is currently listed on the website Banned: "Copy of an enumerated assault weapon".
Like you I believe the rifle should be re-classified as a "copycat" (in stock form) however given the cosmetic similarities to the AR-15 and MSP current classification on their website as a "Copy of an enumerated assault weapon" one would most likely need to hire an attorney to overturn an arrest for possessing an MCX.