This is my number one concern about KNOPPIX(and its derivatives). The modeline in the supplied XF86Config-4 is just not necessary as XFree86 4.3 already has very good in-built defaults.

On my notebook, I needed to delete all of them or else I just got complete lockup, luckily it was not fried.

IMO, this is a case of getting the most impressive display setting(resolution, frequency) that goes overboard and being harmful.