Comment 11 for bug 1728111

"is-leader" does refresh. You can see the details here: https://github.com/juju/juju/blob/develop/worker/uniter/runner/context/leader.go#L54.

If the clock was jumping on the controller, then this could be explained. I've looked over the worker/lease and worker/leadership code, and it should now be sound when compiled with Go 1.9+ (which we now do), from Juju 2.3-beta2+ (new lease manager code).