Unknown query or process is updating hundres of thousands of rows in the `namespaces` table

Since the 10.0 deploy we have been observing an increase in dead tuples in the namespaces table on various occasions:

This puts unnecessary pressure on database vacuuming and wastes space by creating a lot of dead tuples. It's not clear what causes this but we suspect it's related to our new plans feature. Whatever it is it has to stop.

@mydigitalself @joshlambert @victorwu Is this perhaps some API call used by an external tool to manage plans and what not?