A strange bug has been plaguing me for a while now, ever since switching to the Greed MUD source code from Envy. Undead monsters, deep underground, could be damaged by sunlight even though they were nowhere near the sun. The exact source of this problem has been difficult to track down, until finally I realized it had to do with susceptibility to light inherent in the undead and also vampire racial types.
To address this issue the code causing damage by sunlight will now only affect outdoor sectors such as city, field, forest, etc. If an undead monster or vampire is in an "inside" sector, they will not be affected by sunlight, because rooms that are "inside" should not be affected by direct sunlight, which in my mind is the only possible source of this damage.