Half the time I'm in the Play Store viewing a list of my installed apps, my phone will somehow register a touch anywhere randomly on the display while I'm not touching the screen in any way. Initially I assumed it was a busted digitizer, but it ONLY does this while I'm in the Play Store, from what I've noticed at least. My phone does this while unplugged from any charger/cable.
Also, a lot of times while I'm using the phone while charging, the digitizer will freak the hell out while I'm touching it and register inputs all over the screen and very rapidly. I've seen this on other phones as well while using a crappy non-OEM charger, but this phone seems very much more sensitive to what charger you're using. Chargers that worked fine on my Note 2 and my wife's current GS4 make my M8's digitizer freak out. Has anyone else noticed this?
FYI, I can see these random inputs by enabling "show touches" in the developer options. I'll see touches register on the screen without me touching the phone at all in both of the scenarios above.