When redefining model.value it must be bound to the model to keep a runtime reference.

src/Umbraco.Web.UI.Client/src/views/propertyeditors/blocklist/umbBlockListPropertyEditor.component.js

@@ -138,10 +138,10 @@
 
             // We need to ensure that the property model value is an object, this is needed for modelObject to recive a reference and keep that updated.
             if (typeof newVal !== 'object' || newVal === null) {// testing if we have null or undefined value or if the value is set to another type than Object.
-                newVal = {};
+                vm.model.value = newVal = {};
             }
 
-            modelObject.update(newVal, $scope);
+            modelObject.update(vm.model.value, $scope);
             onLoaded();
         }