fungus:
Yep. AVR chips seem quite resilient to having their output pins shorted to ground. It's a good thing too, when you see the abuse they get (keep reading these forums for horror stories...)
I wonder if we are going to see horror stories about people's new Dues being destroyed due them being less sensitive to abuse and because of the 3.3v vs. 5v issues. Shorting out your first Due is a teachable moment, shorting out the second probably indicates whether you ignored the teachable moment.