Confederate Capital of (the District of) Columbia

Very vaguely related to my recent Border-States-as-Pro-CSA thread.

The always-reliable Wikipedia claims that the Confederacy, should it have captured Washington early enough in the war, would move its government to Washington DC and thence admit Maryland.

Did the CSA actually intend to make Washington their capital if they somehow acquired it?
There's a problem with the idea, which I haven't yet seen any of these threads address,

You need to explain HOW and WHY the border state flip happened. After all, it's only a total flip from OTL.

I should warn you that it's not likely to be an easy problem to solve, because OTL's CSA diplomacy (what decides whom allies with what side) was seriously lame, and the OTL path of conquest mostly went the other way. Not impossible, but ir'll take serious thought and research.