I ordered one of the bundles that included the mini-USB shield, the larger USB shield and the arduino footprint shield. If I use the mini shield, I seem to have no problems. If I use the arduino footprint shield and don't plug anything onto the GPIO, I have no problems. But if I use the larger USB shield with-or-without anything on the GPIO or the arduino shield with something plugged into the GPIO, they seem to start up just fine but if I come back a few minutes later, it is powered down and pressing reset and/or flipping the switch will not seem to power it back up. (I have to disconnect the USB and plug it back in)
My power sources should be more than sufficient (they were the largest USB-plug based power sources I could find at the time. One is a 10 port hub with a high-capacity charge plug at 2.5a and the other is a 5-port anker power-hub that I use to power my raspberry pi's. Also capable of 2.5-to-3.0 amp per connector)
Is there something in these shields or the plates that would trigger an auto-power-down mode? This morning I just connected the ethernet connector on the larger USB shield and it still powered down by the time I got to work. The arduino board still seems to be running but only because I didn't put anything on the GPIO.