has a relation starting with "juju-"

[William Reade]

More specifically, it has a (requirer) relation called "juju-info", which clashes with the implicit "juju-info" (provider) relation.

Charms must not have multiple relations with the same name, for obvious reasons; it seems that neither the python implementation, nor the golang store implementation, are checking against the implicit relation, so there are surely other bugs in play -- but this is still a problem for this charm.

"juju-info" is specifically a problem because we'll end up running the (requirer) hooks when we're trying to join/change/depart for the implicit provider relation (and I don't think it's a good idea to special-case the unit agent to ignore those specific hooks in that specific situation); however, we intend to disallow *all* "juju-*" hooks, relations, and (provider-side) interfaces, so that we have space to add further implicit relations/interfaces without risking collisions in future.