A bit more testing shows that using juju upgrade-charm does not cause the version to regress BUT the following will:
* juju deploy bundle.yaml where bundle contains series: <series>
* remove series: <series> from the bundle
* juju deploy bundle.yaml (a common way to upgrade all charms)
So this could be an issue for environments that used juju deploy --series <series> bundle.yaml who subsequently run juju deploy bundle.yaml i.e. without the series (which used to work).
A bit more testing shows that using juju upgrade-charm does not cause the version to regress BUT the following will:
* juju deploy bundle.yaml where bundle contains series: <series>
* remove series: <series> from the bundle
* juju deploy bundle.yaml (a common way to upgrade all charms)
So this could be an issue for environments that used juju deploy --series <series> bundle.yaml who subsequently run juju deploy bundle.yaml i.e. without the series (which used to work).