Cabin Door will not stay open

[John Camacho]

I cannot get the main cabin door to stay open. When I try to open it, it tries to close. When I grab the door from the outside and hold, it will eventually open all the way but not without a fight. When I let go of the mouse button, the door begins to close and will completely close. It's as if I am trying to open it and someone else on the other side is trying to close it. This does not happen often but about once every 5 flights. Any ideas? Thanks!