Is there any use case for querying for pages that have some arbitrary category without saying which category it is? I do not really see what useful information the resulting list of pages could give you, unless you use categories only in a very limited sense (and ensure that all other users do the same).

At the time I posted this bug report, I think what I was trying to do was find uncategorized pages that also matched some specific semantic query. I might have also been trying to organize categories using their own "meta" semantic data.