[PATCH]node/%/questions category sorting

The page node/%/questions, when having some categories, doesn't allow to sort them. I can move categories around all I want or change weight directly, it still would be reset to 1 when saving.

I find out that the line 634 of quiz.admin.inc is responsible for this behaviour.
When I comment out this line:
//$existing['weight'] = 1;
weights are saving correctly.

So the question is, should this line be commented out or is there some meaning to it which I don't see?