In many cases, after the next reboot the machines network interfaces have a different MAC-address -even worse, they all have _the same_ MAC address (00:19:66:97:d7:e2). I tried it in many variations, but could not really detect any system - even under identical circumstances this problem seems occurs very often, but not always. If I restore the original ROM contents (after I noticed the problem, I always saved the original firmware) the machines always get their original MAC address back (but of course also the buggy bios that I am trying to upgrade). The ROM contents of the machines do contain their MAC addresses at a certain offset but in the vendor supplied BIOS image that I flash has all bits set to 1 in this and several other (obviously data) areas, the mysterious "default" MAC address
"00:19:66:97:d7:e2" does not occur in this file. When I flash the file under DOS using afudos.exe ("AMI firmware update utility 4.14"), the machines will keep their original MAC address.(As I just noticed, that program also has an option to explicitly set the MAC address).

Does anybody have an idea, what is going on here? (As I said, the phenomenon does not even seem to be deterministic). Maybe even an idea, how to do the upgrade using flashrom? (The machines are integrated in some Linux-based management system, so using flashrom I could do the upgrade automatic; except for the problem with the duplicated MAC addresses everything seems to work just fine after flashing the BIOS with flashrom).