I'm surprised that it works without power on Vin. Perhaps the shield does not match the schematic, in which case all bets are off. Take a careful look at the shield to see if the pins that are connected are the ones shown in the schematic.
If you add a jumper from Reset to Ground it will be like holding down the Reset button and NOTHING will work.
I would try a wire from Vin on the shield to 5V on the Arduino. That should be enough to power the 3.3V regulator.