Are map entities supposed to change their rate of speed if they collide with a physics object?

Example: a map entity moved with ent_move collides with a physics object. In my tests, the map entity slows down and pushes the physics ball away. Why does the speed of the map entity slow down instead of maintaining its current speed and simply pushing the physics object out of the way? Or is it a bug that the map entity slows down?

thanks for your time,
Jason