Apparently, under certain conditions, villagers aren't recognizing their occupation blocks correctly. The example for what I've been testing is that the butcher in my village won't recognize his Smoker if I place a Wall block above it (as if it were a chimney). Likewise, he seems to continue to ignore it if it has only one block of airspace above it... it would seem that he only recognizes it if there's room for him to stand on top of it. This is very annoying, considering that having a chimney on top of a smoker block per the standard prevents a butcher from using it.