This was driving me crazy!
Whenever I unplugged the device from usb and then pressed the power button to turn off the screen, the thing would turn itself off!

What I found was, me using SetCPU to clock the Tab down to 100MHz when screen off, was actually causing the problem.
so the solution was set the ‘screen off’ profile to a minimum of 200MHz with the ‘ondemand’ scaling setting and all is good… 🙂

“Are you using setcpu? I had the same problem when trying to use conservitave or set the minimum to 100mhz. Currently I use ondemand with a minimum of 200mhz”