diff --git a/src/Umbraco.Core/Models/ContentType.cs b/src/Umbraco.Core/Models/ContentType.cs
index 1cf7fc9684..ec763d07fa 100644
--- a/src/Umbraco.Core/Models/ContentType.cs
+++ b/src/Umbraco.Core/Models/ContentType.cs
@@ -133,29 +133,6 @@ namespace Umbraco.Core.Models
                 Key = Guid.NewGuid();
         }
 
-        /// <summary>
-        /// Method to call when Entity is being updated
-        /// </summary>
-        /// <remarks>Modified Date is set and a new Version guid is set</remarks>
-        internal override void UpdatingEntity()
-        {
-            base.UpdatingEntity();
-        }
-
-        public override object DeepClone()
-        {
-            var clone = (ContentType)base.DeepClone();
-            var propertyGroups = PropertyGroups.Select(x => (PropertyGroup)x.DeepClone()).ToList();
-            clone.PropertyGroups = new PropertyGroupCollection(propertyGroups);
-            //set the property types that are not part of a group
-            clone.PropertyTypes = PropertyTypeCollection
-                .Where(x => x.PropertyGroupId == null)
-                .Select(x => (PropertyType)x.DeepClone()).ToList();
-
-            clone.ResetDirtyProperties(false);
-
-            return clone;
-        }
 
         /// <summary>
         /// Creates a deep clone of the current entity with its identity/alias and it's property identities reset
diff --git a/src/Umbraco.Core/Models/ContentTypeBase.cs b/src/Umbraco.Core/Models/ContentTypeBase.cs
index da4cdcfd19..5c09deadb8 100644
--- a/src/Umbraco.Core/Models/ContentTypeBase.cs
+++ b/src/Umbraco.Core/Models/ContentTypeBase.cs
@@ -351,7 +351,9 @@ namespace Umbraco.Core.Models
         /// <summary>
         /// List of PropertyGroups available on this ContentType
         /// </summary>
-        /// <remarks>A PropertyGroup corresponds to a Tab in the UI</remarks>
+        /// <remarks>
+        /// A PropertyGroup corresponds to a Tab in the UI
+        /// </remarks>
         [DataMember]
         public virtual PropertyGroupCollection PropertyGroups
         {
@@ -367,7 +369,13 @@ namespace Umbraco.Core.Models
         /// List of PropertyTypes available on this ContentType.
         /// This list aggregates PropertyTypes across the PropertyGroups.
         /// </summary>
+        /// <remarks>
+        /// Marked as DoNotClone because the result of this property is not the natural result of the data, it is 
+        /// a union of data so when auto-cloning if the setter is used it will be setting the unnatural result of the 
+        /// data. We manually clone this instead. 
+        /// </remarks>
         [IgnoreDataMember]
+        [DoNotClone]
         public virtual IEnumerable<PropertyType> PropertyTypes
         {
             get
@@ -383,6 +391,14 @@ namespace Umbraco.Core.Models
         }
 
         /// <summary>
+        /// Returns the property type collection containing types that are non-groups - used for tests
+        /// </summary>
+        internal IEnumerable<PropertyType> NonGroupedPropertyTypes
+        {
+            get { return _propertyTypes; }
+        }
+
+            /// <summary>
         /// A boolean flag indicating if a property type has been removed from this instance.
         /// </summary>
         /// <remarks>
@@ -579,5 +595,19 @@ namespace Umbraco.Core.Models
                 propertyType.ResetDirtyProperties();
             }
         }
+
+        public override object DeepClone()
+        {
+            var clone = (ContentTypeBase)base.DeepClone();
+
+            //need to manually wire up the event handlers for the property type collections - we've ensured
+            // its ignored from the auto-clone process because its return values are unions, not raw and 
+            // we end up with duplicates, see: http://issues.umbraco.org/issue/U4-4842
+
+            clone._propertyTypes = (PropertyTypeCollection)_propertyTypes.DeepClone();
+            clone._propertyTypes.CollectionChanged += clone.PropertyTypesChanged;
+
+            return clone;
+        }
     }
 }
\ No newline at end of file
diff --git a/src/Umbraco.Core/Models/DeepCloneHelper.cs b/src/Umbraco.Core/Models/DeepCloneHelper.cs
index aaee03f963..d8ef10751b 100644
--- a/src/Umbraco.Core/Models/DeepCloneHelper.cs
+++ b/src/Umbraco.Core/Models/DeepCloneHelper.cs
@@ -2,9 +2,29 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
+using System.Reflection;
 
 namespace Umbraco.Core.Models
 {
+    /// <summary>
+    /// Used to attribute properties that have a setter and are a reference type
+    /// that should be ignored for cloning when using the DeepCloneHelper
+    /// </summary>
+    /// <remarks>
+    /// 
+    /// This attribute must be used:
+    /// * when the property is backed by a field but the result of the property is the un-natural data stored in the field
+    ///  
+    /// This attribute should not be used:
+    /// * when the property is virtual
+    /// * when the setter performs additional required logic other than just setting the underlying field
+    /// 
+    /// </remarks>
+    internal class DoNotCloneAttribute : Attribute
+    {
+        
+    }
+
     public static class DeepCloneHelper
     {
         /// <summary>
@@ -25,8 +45,10 @@ namespace Umbraco.Core.Models
 
             var refProperties = inputType.GetProperties()
                 .Where(x =>
+                    //is not attributed with the ignore clone attribute
+                    x.GetCustomAttribute<DoNotCloneAttribute>() == null
                     //reference type but not string
-                    x.PropertyType.IsValueType == false && x.PropertyType != typeof (string)
+                    && x.PropertyType.IsValueType == false && x.PropertyType != typeof (string)
                         //settable
                     && x.CanWrite
                         //non-indexed
diff --git a/src/Umbraco.Core/Persistence/Caching/RuntimeCacheProvider.cs b/src/Umbraco.Core/Persistence/Caching/RuntimeCacheProvider.cs
index c2ca53a240..acacadb0cc 100644
--- a/src/Umbraco.Core/Persistence/Caching/RuntimeCacheProvider.cs
+++ b/src/Umbraco.Core/Persistence/Caching/RuntimeCacheProvider.cs
@@ -128,9 +128,9 @@ namespace Umbraco.Core.Persistence.Caching
         public void Save(Type type, IEntity entity)
         {
             //IMPORTANT: we must clone to store, see: http://issues.umbraco.org/issue/U4-4259
-            entity = (IEntity)entity.DeepClone();
+            var clone = (IEntity)entity.DeepClone();
 
-            var key = GetCompositeId(type, entity.Id);
+            var key = GetCompositeId(type, clone.Id);
             
             _keyTracker.TryAdd(key);
 
@@ -139,11 +139,11 @@ namespace Umbraco.Core.Persistence.Caching
 
             if (_memoryCache != null)
             {
-                _memoryCache.Set(key, entity, new CacheItemPolicy { SlidingExpiration = TimeSpan.FromMinutes(5) });
+                _memoryCache.Set(key, clone, new CacheItemPolicy { SlidingExpiration = TimeSpan.FromMinutes(5) });
             }
             else
             {
-                HttpRuntime.Cache.Insert(key, entity, null, System.Web.Caching.Cache.NoAbsoluteExpiration, TimeSpan.FromMinutes(5));
+                HttpRuntime.Cache.Insert(key, clone, null, System.Web.Caching.Cache.NoAbsoluteExpiration, TimeSpan.FromMinutes(5));
             }
         }
 
diff --git a/src/Umbraco.Tests/Models/ContentTypeTests.cs b/src/Umbraco.Tests/Models/ContentTypeTests.cs
index dc2de0d6bb..43b90c424e 100644
--- a/src/Umbraco.Tests/Models/ContentTypeTests.cs
+++ b/src/Umbraco.Tests/Models/ContentTypeTests.cs
@@ -162,6 +162,7 @@ namespace Umbraco.Tests.Models
             }
             Assert.AreNotSame(clone.PropertyTypes, contentType.PropertyTypes);
             Assert.AreEqual(clone.PropertyTypes.Count(), contentType.PropertyTypes.Count());
+            Assert.AreEqual(0, ((ContentTypeBase)clone).NonGroupedPropertyTypes.Count());
             for (var index = 0; index < contentType.PropertyTypes.Count(); index++)
             {
                 Assert.AreNotSame(clone.PropertyTypes.ElementAt(index), contentType.PropertyTypes.ElementAt(index));