The Imperial troopers driving the AT-ST who decide to leave their relative protection of an armored vessel to rid themselves of their piggybackers.
I mean, they didn't know a wookie was out there but still... Shoot the Ewok in the face if he's that big a problem, and just stay within the "tank". Ya don't get out in the middle of a fight though.
But yeah, the Empire makes some assenine maneuvers sometimes. I like the flubs though. Shows the imperfection of coordinating a large military body. There's still some idgits in the ranks that can goof things up for ya.