in some email cases template generates ngRepeat:dupes error

UI/Templates/MailerUI/UIxMailViewTemplate.wox

@@ -296,7 +296,7 @@
             <div class="msg-body">
               <div layout="row" layout-wrap="layout-wrap">
                 <div class="mailer_mailcontent" layout="row" layout-wrap="layout-wrap"
-                     ng-repeat="part in viewer.message.$content() track by $id(part.content)"
+                     ng-repeat="part in viewer.message.$content() track by $index"
                      ng-class="::part.msgclass">
                   <div class="md-flex sg-mail-part"
                        tabindex="-1"