fixes test

src/Umbraco.Core/Models/PropertyType.cs

@@ -178,6 +178,7 @@ namespace Umbraco.Core.Models
         /// </summary>
         /// <remarks>For generic properties, the value is <c>null</c>.</remarks>
         [DataMember]
+        [DoNotClone]
         public Lazy<int> PropertyGroupId
         {
             get => _propertyGroupId;

src/Umbraco.Tests/Models/PropertyTypeTests.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Diagnostics;
+using System.Linq;
+using System.Reflection;
 using NUnit.Framework;
 using Umbraco.Core.Models;
 using Umbraco.Core.Serialization;
@@ -49,9 +51,9 @@ namespace Umbraco.Tests.Models
             Assert.AreEqual(clone.ValidationRegExp, pt.ValidationRegExp);
             Assert.AreEqual(clone.ValueStorageType, pt.ValueStorageType);
 
-            //This double verifies by reflection
+            //This double verifies by reflection (don't test properties marked with [DoNotClone]
             var allProps = clone.GetType().GetProperties();
-            foreach (var propertyInfo in allProps)
+            foreach (var propertyInfo in allProps.Where(p => p.GetCustomAttribute<DoNotCloneAttribute>(false) == null))
             {
                 Assert.AreEqual(propertyInfo.GetValue(clone, null), propertyInfo.GetValue(pt, null));
             }