I simplified my regexp expression to gain insight into what is causing the problem (one of serveral); so far, this one is the simplest expression that does also find titles w/o even any round bracket:
Code:
title:"~\([^()]*?\s+\d+\)"
(of course, the result is somewhat different from my original query...)
Currently, I feel that this must be some bug in calibre, but I would hate to bother the bug list if the problem sits in front of the keyboard.
Anyone?