It appears that ceilings aren't always automatically constructed, even when it's a small enough room. See example (world here (https://www.dropbox.com/s/9x37cx6l0fzqbhg/prob.rim) (the one attached won't work because it was too big apparently)):
(http://i.imgur.com/3uli8eq.jpg)
This dispenser keeps short circuiting in the rain...why isn't it covered?
Perhaps there should be some way to "force" ceiling construction to get rid of this type of problem.
[attachment deleted by admin: too old]
Confirmed fixed in 0.0.254b