Hi again, Brendan.
I too wondered whether 2d simply involved setter error (‘is it’ might suggest a different two letter abbreviation, reversed?).
I also spent a while thinking that ‘break’ might be doing double duty, which I think would also form part of your parsing according to your second theory. Ingenious as it is, I’m not sure that it quite explains the clue, and it would be obscure even for Enigmatist!
And now I see that chrise doesn’t have a problem with 2d. Come on, Chris, please put us all out of our misery!