If the charm can't connect to a configure keystone/swift endpoint, it falls into a "previous install" blocked state

I'm deploying the 'latest/stable' charm from charmhub into an Openstack cloud, as described here:

https://charmhub.io/postgresql/docs/e-legacy-charm

Regardless of whether I deploy to "jammy" or "focal", if I deploy with pre-set non-default configuration options (I plan to narrow down the exact option(s) that trigger this, but wanted to file early), I wind up blocked with the same message mentioned in LP:1831858.

This is a clean install to a single Openstack VM instance, freshly created by Juju as part of the charm deploy.

If I just deploy the same charm to the same series with default config, the error doesn't surface, but if I then apply the desired config with 'juju config --file config.yaml' then I end up in the same blocked state:

postgresql/0* blocked idle 0 10.x.y.z PostgreSQL config from previous install found at /etc/postgresql/14/main/postgresql.conf

I've tried to reproduce this locally with an LXD Juju setup, but oddly enough that seems to work fine (I wonder whether differences in the cloud images might be a factor).

The Openstack cloud is using Juju 3.1.2, my local setup is still on 2.9.43.

I'll set up a Juju 3 local LXD controller for further testing, and will see whether I can reproduce there, and then iterate on exactly which config option is the problem, but that'll need to be next week now.