Wow, that was actually it, thank you very much.
I feel pretty stupid now.

I downloaded bitcoin core 0.12 from github, compiled it and started using.
At one point I got a message saying that I need to use "walletpassphrase", even though I did not encrypt the wallet.
I thought it's because I unwittingly used "walletlock" before setting anything, but it doesn't seem to be possible.
Plus, encrypting wallet requires daemon reset, which I didn't do before the problem started.

Does anyone have any idea what might have happened?