That happens sometimes, and it's not exclusive to the flophouse. First time I ever experienced that was in the Lady's Resting Place. I thought it was a stealthed player or a DM messing with me at first. Sometimes it takes a few tries, but you can usually get out (might have to run out as soon as you open the door). Not sure why it happens though, since it's not happening all the time... maybe lag-induced.