I posted this in bug reports but no one seems to have an answer.
Here's the situation: I took the Black gate from Mordor and left small force as a garrison there. Now Mordor is besieging it from the outside(west) I came back with my main army to reinforce them but i can't seem to be able to attack the besiegers directly with main army, so I attacked with garrisoned forces and the main army came as reinforcements. Everything seems to be going as it should but battlemap is where things go little haywire.
Here's a little diagram to help you understand what's going on. http://s25.postimg.org/6iuv52m9r/Untitled_1.jpg
Blue is for reinforcements green for garrison and red for enemy army. for some weird reason part of one stack comes in from behind and sides of enemy army and main body of the same stack is stuck at the point where they should be coming in from. now i don't know if any of you had the same problem but i'm guessing i'm not the only one. i understand that game mechanics don't allow me to pass around or through besieged gate which is actually a castle ingame but at least i should be allowed to reinforce my garrison from behind right? so what gives? to me this seems to be very important part of this mod so it shouldn't be so buggy.