Is it possible that in RC0/RC1 changed ion icons in some way?
<ion-icon ios="ios-arrow-back" md="md-arrow-back"></ion-icon>
renders in brower to:
<ion-icon ios="ios-arrow-back" md="md-arrow-back" role="img" class="icon-md ion-md-arrow-back" aria-label="arrow back" ng-reflect-ios="ios-arrow-back" ng-reflect-md="md-arrow-back"></ion-icon>
… but is displayed as grey box.