Well, can a muzzy bend, you bet! can it bend on a tree root, yes it can. This can happen to any broadhead, but I suspect that you may have hit somthing a bit harder, and with those "random flyers" I would bet you have an arrow or two that is not setup perfectly, and it also sounds like you don't have enough fletching control. Are you using helical fletching of at least 4" in length? I have bent and broken most every broadhead out there and I can tell you that Muzzys are some of the toughest made, as well as very accurate.

TAKE YOUR KIDS HUNTING AND YOU WON'T BE HUNTING FOR YOUR KIDS