adillon, that's what the F4 command is for, (Cancel Manuever) Which makes them abandon any position you have assigned them and will return to either F1, F2, or F3 depending on what you have set at the moment.
Another invincibility glitch, Once and only once happend to me on Geonosis. in the latter portion of the Last Geonosis Level, there are 2 SBD's that are supposed to be killed by falling debris. The 2nd however never reached his position. (I think because he stopped and crouched to shoot a charged shot at me.) So when the debris fell it missed him. And he was invincible. But he's easily avoided. Just run by him and you'll be fine.
Also sometimes the Wookies on Kashyyyk in the First level get stuck in a running position against a wall.