Many thanks for your explanation, nevertheless, currently there 2 things which I cannot test for the moment, is it true,that you are saying :using DVD-RW would report a correct checksum ( here I know, that at least there is one burning program under WINDOWS,which generates DVDs with a correct checksum ) using DVD-R or DVD+R would be also okay .
Yes. If unit didn't have to pad the file system image as required by specification, then a) DVD-RW Sequential, b) DVD-R and c) DVD+R recordings performed with growisofs -dvd-compat(!) option should pass the 'md5sum /dev/dvd' test. "Should" means "I won't be surprised if someone runs into a firmware that will fail this test even for above mentioned recordings."
In any other combination, namely a) padding to 32KB boundary was required, b) growisofs executed without -dvd-compat option, c) DVD+RW and d) DVD-RW Restricted Overwrite recordings, trivial 'md5sum /dev/dvd' test might *fail*. The failure however won't be violation of any specification or indicate a bug in recording software or unit firmware.
As you can see it's a number of combinations and if you don't want to figure out which particular combination caused the above mentioned checksum test to fail at any particular occasion, always verify as much data as you've actually written: 'dd if=/dev/dvd count=<appropriate count> | md5sum' and not just 'md5sum /dev/dvd'. A.