Document tree macro doesn't group by space when hierarchyMode=parentchild and showSpaces=true

You can reproduce using:

{{documentTree hierarchyMode="parentchild" showSpaces="true" /}}

Expand the entire Main space node first. You'll see that there are descendants from other spaces (e.g. Sandbox).

This document tree configuration corresponds to the old (<7.2M2) Document Index Tree View so we should keep it working for backwards compatibility.