Custom Trust lists have large recursive implications because the ones you trust directly (Depth 0) make you trust the ones they trust (Depth 1), and the users they trust (Depth 2).
I thought I found the one, but I was wrong. I got to go now, if you don't find it I'll look deeper. It could also be someone changed his Trust list after yesterday's trust data dump.
I'll keep looking for a connection between someone I'm trusting the account in question. I realize you compile your list manually and there's some delay. I've found it very helpful, it's much appreciated.
ETA:
I found the connection, I guess I didn't realize the depth of trusted users.