The allowInvalid setting is for changes started from a view, not from a model (see how Angular uses allowInvalid here: https://github.com/angular/angular.js/blob/master/src/ng/directive/ngModel.js). You would need to attach a custom directive and execute ngModel.$setViewValue(customValue).

As for adding baked in support from model changes, I'm leaning towards rejecting this request - IMO this is a perversion of what that option was created for in Angular. In addition, this likely would have unintended consequences with the datepicker and popup that could potentially break the datepicker.

I would be willing to potentially support a PR that adds support for this using a different option unique to the popup, but it also needs to be well-tested along with a reproduction in Plunker demonstrating it works properly.

1. User enters custom date string, saves form
2. User reloads form, date string is hidden, although still in model (which means it can't be reviewed or corrected)

Seems like a very common use case that is completely broken right now, and allowInvalid on any standard form control would behave in a way that doesn't break it. Special-casing the setting, unless there is an unmanageable technical issue, seems like a strange choice.