I agree, I wouldn't bother sterilizing boxes unless they are from unknown origin. And that would be the flame treatment, torch, whatever, and that would be for AFB, and I don't think that the oven is hot enough to kill that.
That there mold will be back in a jiffy, next time the boxes get a little wet. I don't think it is worth the risk of dripping propolis all over the oven(no honey, that really is from the apple pie you made!!), not to mention having the boxes catch fire. But interesting nonetheless.