Bug? ion-nav-button and ion-content seem to have separate $scope

Reproduced here

I’m basically trying to show/hide delete buttons with an “Edit” navigation button.

I define a button, set ng-click="showDelete = !showDelete"
The ionic list has the attribute show-delete=“showDelete”

If the button is in ion-nav-button, then showDelete seems to be in a separte scope compared to the list.
If the button is inside ion-content, then pressing the edit button will show delete on the ion-list.

Can someone explain what I’m missing? I’ve seen other posts where other people have run into it, but there’s never an explanation