Battery Full [Q] Nexus 4 & 7 Wireless charging oddities

Hi. I've got a Nexus 4(rev 11) and Nexus 7(2013 edish) and both are running stock unroofed 4.4.2 at the moment. I'll describe the Qi charger I using at the bottom to avoid clutter. The issue I've been having is that when I place either device on the charger at night, they both seem to charge, and then rapidly discharge once full. Using previous research, the general consensus seems to be that Qi chargers are supposed to stop at 100, and kick in again when the level drops a bit. This seems to only happen for me as I once put my N7 on the charger at 56%, and when I woke up, I found it charging at 22%. When I put the N4 on, it seems to have discharged to in between 65-78% remaining by the time I get up. Can anyone shed a possible reason as to why the devices won't continue to charge?

The charger: GMYLE (TM) Black White Wireless Mini Charging Pad Mat Qi-enabled Standard Charger (1000mA)