Yeah, my experience with the 1640 is the system will hang if you try to access the drive after a flash, without a reboot. Also Windows hangs on shutdown as well, after the flash, but is fine after the reboot. This applies to CVT or Windows EXE flashing, so it's something to do with a soft reset.
Personally I believe that the 1620 and 1640 learn. I know the drive has EEPROM and I typically experience better burn quality on the second burn of a new media code. Also my 1620 started burning coasters with MCC003 only and flashing back to the "L" firmware fixed this problem, so this indicates to me that individual media codes have data stored in the EEPROM