hw6-10: wrong answer evaluated as correct?

In the explanation, Norvig says that the right-most min node (in the third row, counting from top to bottom) should be pruned. I (incorrectly) answered that it shouldn't. I'm evaluated as being correct. Does anybody else have this problem?

EDIT: Now that I've checked thoroughly, I realize I had answered right for the pruning of that node (and its children). A couple of hours before the deadline, I changed my answer. It seems that I have been evaluated based on my previous answer.