Was there an interim version of accounts on git at some point that had just ("acentry", "account") for the key?
I just browsed back through the git commit history, and I don't see any interim commits of the account code (I was working in local branches, and didn't push interim versions up).
davout: You should try dumping your wallet using the latest bitcointools (dbdump.py --wallet), it will tell you if it finds weird key values in there.