Questions unassignable when using filter

Narrowing in the displayed questions by using the title filter causes the question to be unassignable in some cases, i.e. clicking on the checkbox of a search result will not add it to the quiz, but strangely this does not happen every time.
I have made the observation that this applies to questions that are already assigned to the quiz (i.e. when opening the question for editing, it is shown as member of the quiz). However, due to another bug, all questions where unassigned from that particular quiz so here we have two problems: The question browser thinks it's assigned and won't re-add the question, on the other hand, the quiz itself thinks it doesn't have the question.
So for now I am stuck with re-editing the question and unassigning it from the quiz.