Now, it seems i found the immediate reason for this behavior:
While checking the system, i noticed 8 CPUs shown in taskmanager, so HyperThreading was enabled!
I rebooted into the BIOS and noticed that ALL settings were different from what i changed there.
HT enabled, Serial and parallel ports enabled - and SATA not on "hotpluggable".
As sure i did not do this, *something* managed to change or reset my BIOS settings!
It is a Asus P8C WS with the latest BIOS version: 3108