Beware Nero DVD "verify after burning" feature

I’ve got an image file with a zip file inside of it. When I extract the image file to the hard drive and open the zip, the zip is not corrupt. When I burn the image file to a particular flaky DVD+RW and enable the verify feature (whether using NeroCOM or in the Nero Burning ROM software itself) it completes verification without detecting errors, but then the zip file’s CRC fails. It depends on the image I’m using – sometimes the verification will fail when it should – but I need 100% accuracy. I’ve implemented my own verification using an MD5 hash and will be using that instead. Luckily I’m able to read the disc after it is burned without ejecting/reinserting the DVD.

Now I’m worried. If I calculate the MD5 hash right after burning the dvd (without ejecting it) I get one answer, if I eject and re-insert the dvd and calculate the MD5 hash again I get a different answer.