Unable to update max score

Hi all, I have a quiz created using the "import quiz" feature. The questions for this quiz are of "multiple choice" type. Also for some questions, "multiple answers" are correct. I want all the questions to score 1 if everything is correct, 0 otherwize. So the first thing I configure is the "simple scoring" in the question editing form. I also make sure that "multiple answers" is also checked. However I can get to change the "max score" to 1 using the "manage questions form. Whatever I put in the "max score" field, it gets back to a value corresponding to the number of correct answers. Conversely, if I create a question from scratch with "multiple answers" and "simple scoring", I automatically get a "max score" to 1 even if there are more than 1 correct answers. And the issue happens also if I create a question without "simple scoring" and decide to change this settings afterwards. Then it's impossible to change the "max score". Am I facing a bug?