HABPanel: ng-if not working

Hi all,
after moving to OH3.1 I needed to rework how a phone call is displayed in HABPanel. I want to display that information only when call status is not IDLE (so it is either RINGING, DIALING or ACTIVE). This is my code for my custom widget:

  <div class="controls">
    <div class="widget">
			<div class="name">fritzCallStatus: {{itemState('fritzCallStatus')}}</div>
    <div class="widget" ng-if="itemState('fritzCallStatus')=='RINGING'">
			<div class="name"><div class="icon off"><svg viewBox="0 0 100 100"><use xlink:href="/static/fritzbox.svg#phone-{{itemState('fritzCallInfo')}}_100"></use></svg></div></div>
			<div class="valueGroup"><div class="value">{{itemState('fritzCallInfo')}}</div></div>

fritzCallStatus in the first div always shows the correct values (IDLE, RINGING, …) but the 2nd div is always hidden although it should be shown when fritzCallStatus changes. Any idea what is wrong?