Compound nodes appearing at root level

In at least two 7.9 projects, there are appearances of the compound nodes of documents at root level.

In one case, we suspected the renaming of a document to be causing it, but that was not confirmed nor reproducible. Another suspect was copying a document. In the other case, we're in the dark, there we're not a lot of renames in the audit logs.

In fact I'm not even sure it's a repository (SCXML?) issue.