Don't have enough questions in category to create the question Random

I have 3 categories with several quizzies in it and i can test 2 of them , they work properly, but when i try to test third one i got this error below: There are not enough questions in category XX to create the question Random 1. What should i change to get rid of this problem? Seems to be obvious that a user should not be able to add more random questions than the total number of a category, since that there will not be duplicated questions in the quiz. 2. Is this is a known bug? I can't add more questions on the quiz.