I no is sounds exactly like those power issues, however the PI is the only kit with a dedicated power supply it runs fine through all the writes..
It was over an hour running before I thought hey I should give it a reboot.. then bam...put the image on a different card repeat.
I think I wrote the image to 3 cards about twice each yesterday

I'll get to the bottom of it but I really need a second PI to screw with..
Only things I can think of is either a dodgy psu, or the usb hubs backfeeding the PI.
If its neither of those then its probably a hardware issue of some sort.