The Red brick factories which are found all over Chernarus (specifically Kamensk Military) I've noticed that while inside the foyer which has it's own roof, rain clips through the ceiling.

You don't get wet and remain warm while inside, but rain clips through the ceiling. This creates a glitch where if you place a barrel inside the barrel thinks it's outside and will fill with rainwater if left opened.

Sunlight also ignores the walls and illuminates the room as if were it outside.