That was my first thought, but then I saw that other pages were being reloaded and on the question pages themselves the new, extended deadline was visible. So, my supposition was that the entire page was being reloaded.
I didn't bother to pursue the thought further, though, because I appeared to have found a solution by logging out of moodle+webwork, then back in.
Incidentally, how do I force a reload from within the problem's pg-file?
WeBWorK Main Forum
answers in problem set with extended deadline not recorded
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