Fellow Monks,
thanks for you replies. I am well aware that I was in no state of mind to either hunt bugs or post questions.

When later I broke the problem at hand down to a small test programm I found that my first guess actually worked (that making me feel less stupid :-).

The real problem was another regexp from another module from a quite largy (self written) library. Anyway, today, with a fresh mind, I could solve this.

Again: thanks.