% bitcoin-cli help lockunspent
lockunspent unlock [{"txid":"txid","vout":n},...]
...
Temporarily lock (lock=true) or unlock (lock=false) specified transaction outputs.
...
Arguments:
1. unlock (boolean, required) Whether to unlock (true) or lock (false) the specified transactions
I'm not surprised this got screwed up. lockunspent true to unlock and lockunspent false to lock is totally counter intuitive and actually contradicts an otherwise self-documenting command. Given the code (if param[0] is true then unlock, otherwise lock), the command _probably_ should have been named unlockunspent. The Right Thing™ would be to fix the semantics of the first param to mean "lock" rather than "unlock" if the current command name is to be kept. But here's to living with a legacy of bad decisions upon which others have come to rely. :o)
(The Wiki also needs updating.)