Comment 4 for bug 702524

OK... found the issue, and it is hanging over from the package branch original days.

The scanner detects merges of proposals, and will mark the branch as merged if the target of the proposal is a series branch.

However, is_series_branch currently says (in lib/lp/codehosting/scanner/mergedetection.py):
def is_series_branch(branch):
    """Is 'branch' associated with a series?"""
    # XXX: JonathanLange 2009-05-07 spec=package-branches: This assumes that
    # we only care about whether a branch is a product series. What about poor
    # old distroseries?
    return branch.associatedProductSeries().count() > 0

The method should be updated to also check the branch.associatedSuiteSourcePackages()