He should have kept his mouth shut…

Pledged Delegate Switcher Will Lose Seat
(Mr. Super)

This was an ill-advised move not just because it breaks the pledge Mr. Johnson took earlier this year, but because there are safeguards built within the Democratic Party rules which allow campaigns to protect their delegates. Mainly, each campaign may review its delegate lists and scratch people off who they think are at risk of not upholding pledges.

When a delegate is elected at a district level organizing meeting, there are also alternate delegates elected. The alternates are selected as back-ups in case the chosen delegate cannot attend the convention, or in case the campaign scratches a delegate from the list.

Looks like an alternate just got bumped up to delegate status in Maryland.