Can't find KNOPPIX filesystem - probably a bug in DVD ed.

Hi, guys. I'm the owner of site www.knoppix.ru, distributing Knoppix CD's and DVD's in Russia and nearby countries. Since the release of Knoppix 5.1.1, i'd getting multiples responses from users about such a problem: Knoppix DVD stopped loading because it can not find Knoppix filesystem. The investigation led to these results:

1. Original ISO are correct and all DVD-discs are recorded correctly. Error is not depending on the writing speed and with the same regularity appears on DVD's (DVD-R), recorded with 8x, 4x, 2x and 1x speeds.
2. One can AVOID ERROR and boot Knoppix succesfully if loading without entering anything in bootup-line of Knoppix. Put the DVD in DVD-drive, reset and wait for KDE starting without touching the keyboard - and all works. BUT trying to boot Knoppix with any type of cheatcode causing the same error ("can't find Knoppix filesystem").
3. It seems that the same DVDs boot up succesfully on older PCs (earlier Celeron's and so on), but can not boot on modern computers.
4. Some users report that they can avoid error by loading in 'expert' mode.

I've searched in many FAQs and didn't find solution. There are similar situation with erroneously recorded DVDs, but they did not loading even without cheatcodes. In my situation avoiding cheatcodes results to successful booting.
I've wrote to mr.Klaus Knopper a month ago, but yet did not get a response. Possibly, Klaus too busy to answer and already knows about this problem, but i can't be sure.

So.. can anyone post this problem to Klaus? Or may be there is a solution, about which i don't hear? I will be thankful for any advice.

WBR, Eugene Zolotov (sentinel @ knoppix.ru)