Indeed, a nav-bar should be used for one navigation system. Any view stack should be considered a navigation system, no? Why would ionic be opinionated about whether a specific view stack is worthy of a working navigation bar or not? Clearly multiple navigation bars are intended to be supported, since $ionicNavBarDelegate exists, and gives us the ability to interact with multiple nav-bars via a handle.
A couple of betas ago a nav-bar in a modal worked out of the box. Now, we need to manually interact with it via $ionicNavBarDelegate to make it show, set the title, etc, as described here in a thread I started a while ago:
Since this worked normally (as per the docs) in a prior release, it sure seems like a bug to me. I created an issue for this a week or so ago.
For illustrative purposes, here are a couple of examples of navigation stacks inside a modal in some fairly high-profile, popular apps.
Nest’s thermostat settings:
Yelp’s signup modal:
Zillow’s settings modal: