Space visible in tree (and node browser) but not in parent space

A symptom of this problem is that it is possible to see a space in the Navigator pane, but that space does not appear in the main panel of the web client.

Renaming and/or copying the parent space of the affected content remedies the problem, but a FULL re-index alone does not.

The issue is intermittent and it is not reproducible at will, but is possibly connected to the load on the system at the time of the original upload of the content.

After discussions with AndyH, I believe that the cause is somewhat understood.