Does the keyboard have a "Sleep" button or software programmable function key? Couldn't tell from the picture on Newegg. If it does, disable it if you can and see iof the problem stops.
It has nine functions, Home - Mail - Search - Play/Pause - Plus (Sound) - Minus (Sound) - Mute - Calculator - My Computer... but no sleep or shut down button. it's really odd.
I also checked the event log, to see what happens at the moment, and sure enough it just says, "Sleep mode -- caused by button or lid." But it's simply not the case, because when the device is unplugged, no issue.
Thanks for the quick reply.