If you file a bug in a source package and then target it to a distro series (say Jaunty, which is the current Ubuntu development series) and also target it to Intrepid (an old series) and then close the Jaunty task (which is the master task in this scenario) the bug will disappear from the ubuntu/+source/$sourcepackage, even though the other task for the package is still open.
Since both of these tasks are on the same package (albeit different series and therefore different BugTargets) Launchpad should be smart enough to realise that the bug is still open on that package and show it in the general overview for that package, including series information as appropriate.
This also holds true for targeted BugTasks on Products and Distributions.
Is this not a duplicate of bug #216668?