Bug, I hope.
Create a multiple choice question.
Select 1 item as correct
Opt to vary points by answer. Give an incorrect selection a point value; give the correct selection a 0 value.
A student who takes this and selects the correct selection has the question marked correct but gets no points. A student who selects the wrong answer with a point value gets the question marked incorrect but gets points.
This cannot be desired behavior. I'm thinking some logic-checking when the question is created would be in order.