Vin < 6.6 volts with USB plugged in, bad idea?

Hello,
The specs for the Arduino Uno say that Vin can be powered from 6 to 20V (See the “Power” section. http://arduino.cc/en/Main/ArduinoBoardUno ). There is a comparator that connects the power to the USB +5V line when Vin < 6.6V, but at that voltage, but if you have , say, 6.3V at Vin, then the 5V regulator will be shorted to the USB +5V line. Isn’t this a bad idea?
-Mike

The comparator looks for Vin/2 to be less then 3.3V. Less than that and the FET FDN340P opens to let USBVCC flow into the circtuit. If Vin/2 is >3.3V, the FET is closed and prevents 5V from the regulator from flowing back into the USBVCC source.

CrossRoads: The comparator looks for Vin/2 to be less then 3.3V. Less than that and the FET FDN340P opens to let USBVCC flow into the circtuit. If Vin/2 is >3.3V, the FET is closed and prevents 5V from the regulator from flowing back into the USBVCC source.

So when Vin is 6.3 V (which is still in spec according to the published specs), then Vin/2 = 3.15V, which is less than 3.3V. 6.3V is also sufficient to power the 5V regulator, and so now both the FET and the 5V regulator are on, and they're not going to be at exactly the same voltage so there's going to be some current flow one way or the other.

Yes, there does seem to be a small range where there could be a conflict.