Wikibase takes ownership of the namespace reserved for Items (as well as those for other Entity types like Properties, Lexemes) - the main namespace on Wikidata. It prevents moving of pages there. This behavior of taking over the main namespace is not correct on Commons. It leads to the main namespace on Commons not being move-protectable. That's bad!
We additionally need to check:
- Is the main namespace hardcoded here? Wikibase allows Items to be in a different namespace and the move protection imposed by Wikibase should trigger there, not always the main namespace.
- Wikibase only triggers its own move protection in the Entity namespaces it is responsible for.
Today, https://commons.wikimedia.org/wiki/Hauptseite was (accidentally?) moved by a non-sysop. The most recent entry in the page protection log includes a move protection for non-sysops ([edit=autoconfirmed] (indefinite) [move=sysop] (indefinite)), so actually, this action should not have been possible. However, the page information does only show the edit protection and no move protection. When trying to protect the page, there is no option to set up a move protection, the only option is edit protection. The same issue applies to other pages in the gallery namespace and is not limited to this page.