Firmware updates are usually to increase media compatibility and affect write strategies adopted in writing or reading a particular media.
You may want to check cdfreaks.com if this is a known issue with your firmware (some firmwares may be flawed...so the adage used often in flashing ... if it ain't faulty, don't fix it

).
Also did you try a different media?
(btw, manufacturer's leave the onus of flashing on the end user and don't usually make amends if a drive has been improperly flashed)
The same site (cdfreaks.com) has links to firmware which may probably resolve your problem.
Then again, if you have doubts in flashing and your drive is in warranty, it doesn't hurt to directly query the manufacturer or seek repairs from a service center.
And any case, I don't recommend burning dvds directly from windows explorer or even using packet writing (nero incd / roxio directcd) in any form.