Just bought the house and I don't really know anything about roof work. After some stormy days we noticed a ceiling water spot. A vent flashing is the most likely culprit far as I can tell; there are other vents but they don't appear to have any issues. The problem one was not nailed or caulked to anything; it can wiggle freely with hand force. The collar part was slightly inverted around the pipe, allowing water to pool right at the seam, whereas things I've read indicate that area should be caulked too. Is there a circumstance that would make it right to leave the whole thing unsecured, or did someone screw up?