I constantly get back to my SP3 and find it running even when I turn it off.

I close the smart cover, it goes to sleep.

I press the power button, it goes to sleep.

But somehow (sometimes) when I go back to use my SP3 it is running, hot and battery drained. I don't know how or why it turns on automatically from sleep. I am assuming that when it is in my bag or on table the smart cover lifts up and I press a button which turns it on without me even knowing about it.

Does anyone know how I can disable all the buttons when in sleep mode, except the power button. I would like to only use power button to make SP3 sleep and wakeup.

Thank you for your help. Really appreciate any input.