Well i had this problem with an internal NEC 3500AG drive the v2.TD flash stopped at 8 but did say the latter drive had been flashed. A few days later i tried to go back to NEC 2.19 but could not flash it, and had multi colour scrambled blocks on pc start screen. The pc would not boot, i was only able to reflash the drive to NEC 2.16 then later to NEC 2.19 after pc rebooted into windows.
Would it not help these flashers to be needed a power off the pc as the NEC firmwares do it, instead of a reboot.
Am now using NEC 2.19 still but do swap when i have to backup some more dvds but not since using v2.TD until this hang problem is fixed.
I have since reflashed to NEC v2.18 and back to v2.19 a couple of times to see burn differences with no problems and no differences all ok.
I have flashed this 3500AG many times over and never a problem except with v2.TD so far. It would be interesting to see if any other internal 3500AG drives owners have noticed this happening, a pre bug report for a fix.
Other thing of note is after using the v2.TD i noticed that other flashes do not show new device found. As always used to do before v2.TD on pc restart after a flash. Maybe something or nothing, but at least the drive is still reading and burning.