tinman13kup:
Not super common for a tantalum to up and burn without underlying cause, but I guess it can happen. You might try pulling it since you are using the regulator on the shield.
I just put the NANO on a breadboard and tried to power it up using the Vin and GND pins but nothing happens. I have some tantalum caps here and will try to exchange it and see what happens on the next power up.
Thanks