Comment 2 for bug 857109

Actually, I misunderstood. I think I get it now:
the invalidated tasks are 'ubuntu' tasks, the fix released ones are 'natty' ones - note that one is a distro context, the other distroseries.

So, seriesonlytasks would help this, because you could file on precise and retarget to natty (rather than nominating to natty).