Since the roadmap serves to gauge the progress of a release, then leaving out items resolved in it will skew the progress percentage. For example, issue 7508 (http://www.mantisbt.org/bugs/view.php?id=7508) is resolved in 1.2.0a2, but never had a target version set. On the roadmap page, this item doesn't show up in the roadmap, which at the moment has 1 resolved and 2 open items. The percentage shows as 33% complete, but if you consider this resolved item, there are 2 resolved and 2 open items, meaning the real progress is 50%. (This does not factor in other resolved items for that release).
On my site, I find myself making sure that all issues have a target version, to ensure the roadmaps are as accurate as possible, since some of my clients use that to gauge project projress, and I don't want it looking like less progress has been made than there really was.
I was thinking of tweaking the code to include not just issues targeted at a particular version, but also issues with no target version that were resolved in that version. But if this is a feature others agree would be useful, then I'd rather let the MAntis pro's do it, and not have to re-modify my own code with each new release
Perhaps a new variable would be suitable, to make this an option? Such as $g_roadmap_include_untargeted_resolved_issues?