After several times I successfully open and close a database protected with OtpKeyProv, Key File field in Open Database dialog doesn't show an option for OTP, only "(None)". And there's no obvious option to re-enable it in that dialog.
Full restart of KeePass solves the problem.
Keepass version 2.25, Windows 7 x64. OtpKeyProv 22.214.171.124.