I have a relatively new (bought 6 months ago) Pavillion 23bw monitor. It may have been doing the following from the beginning:
At the end of the day, I shut down my computer (HP Envy). After the computer is completely off, I turn the monitor off with its power switch. This may be before or after it has gone to sleep. Doesn't matter.
In any event, the power light goes off (from light to dark, or from orange to dark).
Hours later, I find that the monitor has turned itself back on, and is now in sleep mode (orange). If I power it off again, I think it will stay off.
Everything else works fine.
I also have had the power switch lockout from time to time, but I have ignored this and it goes away by itself.