I think they always want the infinitive (“to [verb]”) form when する is included in the vocabulary card, but there are times when する is omitted that the answer they want is not a straight noun but instead a gerund/participle (that is, a verb with an -ing ending that’s acting as a noun or an adjective). A couple examples:
I understand that gerunds function as nouns in English, and sometimes it doesn’t ping me as awkward (cleaning’s a good example of this), but I find some of them kind of odd choices, and they do trip me up on occasion. Questioning, for example–I got that wrong often enough that I added a synonym (interrogation).