Yes I have seen that a few times.. looks like communication works, but HDTuner is not responsive. Reset the USB will not fix it. it is almost like we need to use an output pin for the switch source for the tuner. Let the Shield control when the tuner gets switched 12v I will probably do that once you get outputs working..
Maybe once the shield is powered have a 15 sec ( or adjustable) delay to turn on the HDTuner..