I solved this by creating a different-enough new version of the question (by switching around some code-blocks), then edited the question, once posted, back to its original format.
I've discovered another variant of this question that was closed as status-bydesign, however I'd like to re-raise this. As a 10k user on other sites, I forgot I wouldn't be able to edit the deleted post, and didn't realise I'd have this duplicate problem. New users presumably wouldn't expect this behaviour anyway. Since there's a clunky way around it anyway, why not turn off de-duplication on owner-deleted questions?