Windows does not support wake by keyboard which is basically what the bezel button is emulating, the keyboard Windows key. So, it's odd that if it is really in sleep mode, that it would wake it up.
I'm not sure that this statement is correct. While it is not clear as to which brand of Windows 8 tablet the OP owns, at least according to the
Microsoft Surface website it appears that pressing the Windows key on the bezel of a Surface will wake the tablet:
There are a few ways to wake Surface:
- Simply open your Surface Typing Cover if it’s closed.
- Press any key on your Surface Typing Cover.
- Press and release the power button on the top edge of Surface.
- Press and release the Windows button at the bottom of the Surface touchscreen.