you might want to try updating to the 2.7.4 firmware as doing so solved the same reboot / lockup problem that I was having, although I was not using a USB hub, just a flash drive.
I am going to try installing the 2.7.1 firmware and see if that improves the issue. the update states
"-Improved USB reliability
USB drives should mount more reliably now.
USB Wifi cards should be better recognized and should always enable on boot (Tested with ALFA NHA)."