It works but I have to be quick because Cashew is incredibly smart. So I have to attract him in again. The first 2 weeks he used to meow very loundly for about 20 to 30 minutes once alone. But in the last 3 or 4 days I noticed that he'll meow a bit in protest, but only for a few minutes. It's obvious he understands that he won't come out until morning.
Cats are smart.
For those wondering why I lock him into the bathroom at night, you have to understand that he becomes a full-attack kitty after about midnight. He'll happily lay on the bed for the night, but if I slip under the covers he'll go nuts, attack my feet sliding under the covers, and try to violently bite them. I can have some quiet time. Evolution provided mammals with ears that are active 24h a day for protection against predators, but now it's no longer necessary I think. I took more pictures in the last few days and I'll upload them on the Web servers as soon as I get them.