spontaneous reboots in jumpdrive mode

[flynx]

I'm trying to make a backup image of my PP.  I press the power button and then hold 'volume up' until I get the blue light.  I connect the phone to my desktop and the volumes appear.  I start a dd command to copy the phone's internal volumes to an image file on my desktop.  It runs for a few minutes, and then the phone spontaneously reboots long before the dd is complete.  AFAIK, this would also happen if I was trying to write an image from the PC to the phone.  Am I doing something wrong?