With the 'BBCode links open new window' option enabled, links within new posts still open in the existing window. Looking at the html output, it doesn't appear as if the target="_blank" attribute is being added to the links.
Here are the set up details:
Server: Apache 1.3.41
I'm running 1.0.4 on another forum (same server), and have tried the OpenSourceCMS demo, but both also suffer the same problem.