Pyquiz allows more than one correct response to be selected when creating selection item

In creating several quiz items by duplicating an original one, I accidentally left the previous choice marked correct after marking an additional one. Both items remained selected and the system did not warn me when I clicked submit. In fact, I only noticed this when I duplicated the erroneously marked item and the duplicate also had two items selected.

I don't know how this behaves if the quiz is deployed, but Pyquiz should not permit it to happen.