As per today, users are able (under certain restrictions) to issue a db1.from.renameCollection(db2.target) request  where from and target are namespaces belonging to different databases.

Under the hood, the request is served through the following sequence of steps:

1. a db2.tmp<randomSubfix>.renameCollection gets locally created
2. existing documents of db1.from get inserted into db2.tmp<randomSubfix>.renameCollection
3. the local catalog commits a db2.tmp<randomSubfix>.renameCollection -> db2.target collection rename with dropTarget: true

Both the creation of the temporary collection and the insertion of the cloned documents produce op entries that are incorrectly visible to end users of database-level change streams.