The motor in my Stir Crazy® corn popper moves both ways. Is this normal?

Yes. The motor used in the Stir Crazy® corn popper is a synchronous type motor which can operate in either direction. Because of this, it is normal for the motor to operate in either direction, and it may automatically reverse itself if presented with an obstruction, such as an unpopped kernel becoming caught between the end of the stir rod and side of base.

Kernels get stuck under the knob, is this normal?

This may occasionally happen, it will not interfere with the popping.