in update:
I did the Alix firmware upgrade. And I did fresh 2.1.3 install on a new 4G CF card. For now it looks like all is fine again :)
I was thinking to do some extensive testing on the old CF, but lacked motivation (After all, all it took was some time + price of the new CF. Though I really hate problems without hard-pointed cause… >:( I guess I'm going to blame the CF anyway and get over it ::))