The owner field should be an URL. Fixes delays in iCal.

radicale/ical.py

@@ -389,6 +389,13 @@ class Calendar(object):
         with open(props_path, 'w') as prop_file:
             json.dump(properties, prop_file)
 
+    @property
+    def owner_url(self):
+        if self.owner:
+            return '/{}/'.format(self.owner).replace('//', '/')
+        else:
+            return None
+
     @property
     def url(self):
         return '/{}/'.format(self.local_path).replace('//', '/')