Go to the second floor in a building and if there is a door in the same spot under(In the first floor)if you click the action button or scroll to "open door" its the one witch is under you that will be affected by the action.
EDIT 1; This happend in the new big office buildings, the ones that only before had the glass entrance. Its a big white building with 3 or 4 floors and long corridors at every floor. This happend in the one west of Elektro. (Industrial area)
EDIT 2; Reading comments and playing some more I can confirm that this also happens with other buildings with several floors.