It's nothing about wandering in. There are only a few things known-- Of people that are gone for a time, they're generally sleeping unnaturally for a length of time, kept elsewhere in the institute for purposes unknown, or have been "released" and then return.

For the former two options, the patients in question regain most or all of their memories. Of the last, there is a chance that when they return they might not recall anything that happened in this place.