When you're within range of the exit you get dispelled - channeled abilities and what not are turned off. For some reaosn the tab screen also becomes inaccessible when you enter the area. Unlike abilities, you don't get the tab screen back if you leave the exit zone. It remains permanently disabled for the remainder of the mission. If someone would map out a mission in a survival, find the exit and happen to walk into the trigger zone, but then needs to stay in the mission for a longer period of time, they'll have to do so without that nice and quick progress check. Seems to happen in any mission - spies, survivals, etc - and any tileset. Tested on Kappa, Sedna (Spy), Cambria, Earth (Spy), Apollodorus, Mercury (Survival), Roche, Phobos (Exterminate).