The first problem is due to the bounding box. The default box has a fixed size for c_move. For physics movement, better set it up to the real size of the actor, either in WED, or with c_setminmax.

The second problem with the scaled terrain doesn't happen here. The vehicle sample and other samples use scaled terrain, and they work fine. Can it be the same reason as your bounding box problem? if not, can you upload a small example where we can see the problem?