My Panasonic plasma changes inputs any time I push any button on the Roku remote!
Try the folowing: settings> system> control other devices(CEC)> uncheck 1-touch play box
For some reason, it seems my Ultra LT remote is more "touchy" along the side where the volume and muting buttons are than the ones I have on the StreamingStick+ remote. Just try holding onto the remote, along that side, a bit differently.