I think this may be a bug. I have noticed some sets I created showing up without the correct hideScore setting when creating them from a definition file, but not double checked that it's a problem with the definition file not being imported correctly. In that you're reporting something that sounds similar (and have checked) it's most likely that it's a bug in the import. I'll try to look at this shortly.
So, shortly in this case means "in about two weeks, when the semester has started to wind down." It looks as if the problem is, as expected, in a column describing the set not being set correctly. Not as expected, it turns out to be a different column than the hide_work column. I'm working on getting a fix into the repository. In the meantime, I believe adding the lines
# this is a default value that we need to have things show up # correctly; it should be the default in the database, really. $newSetRecord->hide_score_by_problem('N');
In ProblemSetList.pm, at line 1672, and in ProblemSetList2.pm, at line 1743, fixes the problem. Line numbers are correct for WeBWorK 2.7.