> Actually this seems like a very strange filesystem /hw problem. The > wal segments keep "changing" even after I stoped the database and > noone is supposly accesing it:
I've seen this before. It was bad RAM. I bet it's a hardware problem for you as well... either bad RAM or a flaky disk.
In my case, I found it out because I got syntax errors in the PostgreSQL logs: SELGCT was not a valid keyword. It turns out that the flaky RAM was flipping bit 1 occasionally, so it would randomly add or subtract 2 from a byte.