Filter on planning

Hi,
On planning view, imagine a phase task "A" that is the parent of some sub tasks and some milestones.
(parent activity is set to "A" for all sub tasks and milestones)
If an advance filter "parent activity" is set to "A", then sub activities are visible, but the milistones disappear.... Which is really a problem.
I've tried to put milestones as activities with a 0 duration. But that's not allowed.

OK, I can understand for meetings and so on. But not for milestones as milestones are usually critical dates from a project management perspective. For improvement ? I hope so.