I have a motor shield and a usb shield in my TinyDuino stack, and I was trying to debug why my motor shield was shorting out intermittently.  I thought maybe I had done a poor job of soldering the power or motor connectors onto the motor shield or that I had blown one of the boards somehow.  Then I discovered that the bottoms motor shield connectors were touching the metal of the usb port connector, and thus shorting out.  I fixed it by restacking the boards so the use was on the top, but then realized that almost anything stacked above the usb shield will end up shorting out on that usb port connector.  So, I hace "fixed" the issue by inserting an unused proto board above the usb shield.

Anyone encounter similar issues?  Maybe the power connector for the motor shield could be offset to the left or right in future revs of the board?

-Mark

Were you using the bolts and spacers?  I just wondering if possible shorts against the USB plug housing might be reduced by maintaining spacing at the "toe" end of the board.

I have not used the motor board, but never had a problem of the boards touching with the screw and spacer set. Perhaps a small square of electrical tape over the portion of the USB connector would solve your issue.