Thank you all for you help. It just confirmed my suspicion that this was indeed a bug. The Version I have is 5.8.0. As for those who tried to explain why this regular expression is problematic, this regular expression is fine and was specifically designed to test this very specific thing. And there is a nice use of (X)* (where X is any other expression) because it gives you the last occurence of pattern X (at least in my version of perl).