I was up on my roof investigating how bats are getting in, when I observed the following:
There are no leaks... yet. Due to presence of yellowjackets, I didn't take a long look, but it appears that when the roof was replaced 17 years ago, they put the shingles under this flashing. I couldn't see if they added new flashing under the new shingles. Then they loaded it down with caulk, and nailed it.
The caulk is failing, and many of the nails have popped up.
Is this something I should be concerned about? How do I address something like this?
Bonus question -- what would cause this, and should I be worried about it?