First I'd like to say that this is with the "set angle" property of the bullet behavior set to "No". It should allow a sprite's angle to be changed and not change the angle of motion.
The bug is the angle of motion of the bullet behavior is independent of the sprite's angle only when the sprite's angle is 0.
Tested in Firefox 10.0.2.
It should be fixed if this: ..\behaviors\bullet\runtime.js line 72