Taxonomy entries are spawning copies of existing entries with the new title as the existing ID, since upgrade

I’ll answer this myself, though kudos to @jacob-peattie for noticing the selection box was non-standard and a likely culprit. So we had the ‘Radio Buttons for Taxonomies’ plugin running (up to date) with the affected taxonomy types selected there. When we removed the taxonomies from there, the problem stopped. But we wanted radio buttons here … Read more

How can I get a plugin to hook ‘dbdelta_queries’ — a filter used during version update?

Must-use (mu) plugins are loaded during the version update process, unlike ordinary plugins. Explanation here. So it’s possible to hook dbdelta_queries and the related filters from within a mu plugin. (Thanks to Sergey Biryukov for the answer.) But, some plugins use the same dbDelta() function as core update, so it’s possible to get queries for … Read more