I bought a Wii U Pro controller months ago. It's an excellent controller.
However, lately I have noticed that when the system is off, the Pro controller will continuously flash the four blue lights, as if it is trying to sync. Also, even if i have no intent on using the Pro controller, it will automatically connect itself as the first controller whenever I turn on the system. Previously, the controller stayed off unless I pushed a button while the system was on. But now, it seems this controller has a mind of its own; it even stays on if i put the Wii U in Wii mode, which is making Wii mode. glitchy as a result.
I am not saying that this is the cause, but until I plugged the Pro controller into the Wii U to charge it for the first time, I was not having these problems.
Thanks!