When I tell a unit to move if there is another friendly unit in the way it goes around. In open terrain this is fine but if it's blocking a small pass the unit tries to go all the way around to get by. It should simply go through the square that is already occupied since it's your unit.

I can manual tell it to move onto the space with the other friendly unit then select it in the newly formed group and tell it to move out. This is a bit annoying as the same thing happens with cities though their is already a thread on that topic.