And the final test has been run:

+ No swap
+ Original Nokia Card
+ Reflashed with lates 2006ED

=> The unit still behaves totally eratic being extremly slow one second than racing ahead and adding the same character dozends of times. No matter how "loaded" the maschine is, this happens even with only WiFi Config running.

Guess it's a Brig. We'll see wether Nokia gives a guarantee, otherwise I get a nightstand and use my MDA/PDA WinCE unit even more.