Objects not moving like expected.

[vidjogamer]

Here is my situation: I have a cube falling onto a large plane acting as the ground. I can apply a force north, west, south or east with w,a,s,d respectively. This works just as expected unless I wait for a brief amount of time almost as if the cube "settles in". Then the keys do nothing. I can not seem to figure out why or how to remedy this. Any advice?