A child Instance of an Instance does not display in All Things

(Bug, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Data Model, User Interface
Summary: This is hard to set up, but if you manage to create a child Instance of another Instance, it won't show up, so it's hard to know it's even there.
Found this by accident in the (very old) A Respectful Calm Space. Only discovered it when I tried to export and reimport that Space, which blew up.
Do we want to support child Instances of Instances? The original idea was yes, and it's beautifully powerful in some extreme edge cases, but we may want to formally not support it until and unless we're ready to take it seriously. (Which will require compelling use cases, and I'm not sure there are any outside of game / simulation situations.)