Additive-only _trackedRenderTags in HdDirtyList?

Hi team,

We notice that when HdDirtyList::UpdateRenderTagsAndReprSelectors updates tracked render tags, only new tracked render tags will be added into _trackedRenderTags. That means, reduced render tags will never be removed from the list and they will still be synced.

Interestingly, there is a comment saying:

    // XXX The additive only nature of this policy can result in more Rprims
    // being sync'd than necessary.

So obviously it is a known issue and we are curious if this behavior is kept for any reason, or we have a chance to improve that.

Thank you,
Lumina Wang