Branching model UI bug - auto-merge toggle can incorrectly be in disabled state

If you go to the Branching Model page for a repository with default settings, and deselect the Release branch checkbox then "Enable automatic merging" becomes disabled as expected (as neither condition for auto-merging is met).

However if you now select a Production branch the "Enable automatic merging" checkbox remains disabled, even though it should be enabled in this state.

You can get it back by toggling the Release checkbox on and back off again.