Since i cannot recreate this possibly due to actually buying the building, it won't work for me again, sadly. Apologies,
and is availabe in vanilla. (the only mods i added later in the game are, 256 Recruitment Limit, Recruitable Prisonersand TameBeasties. None of these should have affected my testing but I might try again sometime with no mods since starting the game with mods might have affected things.