I hope it isn't that. I only have one add-on on my machine and that is GB's Editor update. I have had no problem going up and down the ladder in the mission editor. I thought I had tested it to death, but then on a start to end run through of the pbo version I just don't get the action. This occurred about 3 hours (mission time) into the mission. Probably the best I could do is get there in a bit over an hour into the mission, so you can see I can't live test it that often.
I thought it might be something to do with the fact that prior to getting there I had added and then removed some actions from the player. I have not tested that yet.
I am beginning to feel a work around is needed.