Wintergrasp siege engine

[Gremriel]

Maybe this has been covered before, but i couldn't find it, so excuse me if there is an answer posted already.

When in Wintergrasp, I sometimes hop on a siege engine which is controlled by someone else. Thing is, whenever i'm on one, for the life of me I can't figure how to get of off it again. I avoid hopping onto one, but in the heat of the battle, I sometimes click when the cursor is the green arrow, and then i have to wait untill the siege engine is destroyed or the game is over...

Not sure it's a nUI thing, but if someone could tell me how to get of off the siege engine, please tell