I have an iPad 2 and i think there's something wrong with its lock-screen button.
As far as i know, 1 tap on that button should lock and turn off the screen but it doesn't work on my iPad.
I thought "OK, it seems that button is dead"... but NO! It works because when i hold the button bit longer, iOS asks me to slide the bar in order to turn my device off.
I have also tried locking my screen by "software" button available in AssesiveTouch but it doesn't work either.
Just to add - I have tried to reset my iPad, restore iOS from the beginning and it didn't work.
The only way to lock it is to set the auto-lock to turn the screen off after few minutes.
I forgot to add that screenshot (home+lock-screen) works without any problem.
Do you maybe know what's happening?