From STW I can say that hold position is a blanket order which orders a formation to move straight toward the **latest ordered position** regardless of combat friction.

If you have a unit of spearmen standing in place on hold formation, and some Feudal Sergeants come up and push them back, the Spearmen will keep moving and pushing to their original position until when and if they get back there.

If you have a unit of spearmen on hold position and order them to move forward to said spot over yonder, and they are charged by some Peasants along the way, they will continue marching toward the appointed spot, fighting along the way, until they either reach it or rout.

This is the way it worked in STW. I can only assume it works the same in MTW, though I do not own the game.

Del