Water will still move through building paper. Sounds like you have a moisture issue in the area as Square Eye said..
Dryer vent?hole in ductwork, water pinhole pipe leak, anything where water can settle in that area from a leaking window or door?
There are all kinds of things to look for, but what it usually boils down to is always moisture if wood buckles.
Look around and post some more pictures, we''ll help the best we can.