> I have filed problem report kern/35120 in this respect.
> Seems ICH8 is not yet fully supported.
>

PR kern/35120 can be closed. It was a hardware problem:

I removed the AENEON (1Rx16 PC2-4200U-444-11) memory and
replaced it with KINGSTON (PC2-4200 CL4 240).

-> The system no longer drops into debugger.

One question remains: is there a reliable memory tester? Memtest86+ wasn't  
in this case.

Kind Regards
Thomas Feddersen