Fixes: U4-4926 Pre-values need to be cloned in/out of the cache

src/Umbraco.Core/Models/PreValue.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Represents a stored pre-value field value
     /// </summary>
-    public class PreValue
+    public class PreValue : IDeepCloneable
     {
         public PreValue(int id, string value, int sortOrder)
         {
@@ -37,5 +37,12 @@
         /// The sort order stored for the pre-value field value
         /// </summary>
         public int SortOrder { get; private set; }
+
+        public virtual object DeepClone()
+        {
+            //Memberwise clone on PreValue will work since it doesn't have any deep elements
+            var clone = (PreValue)MemberwiseClone();            
+            return clone;
+        }
     }
 }

src/Umbraco.Core/Models/PreValueCollection.cs

@@ -14,7 +14,7 @@ namespace Umbraco.Core.Models
     /// Most legacy property editors won't support the dictionary format but new property editors should always use the dictionary format.
     /// In order to get overrideable pre-values working we need a dictionary since we'll have to reference a pre-value by a key.
     /// </remarks>
-    public class PreValueCollection
+    public class PreValueCollection : IDeepCloneable
     {
         private IDictionary<string, PreValue> _preValuesAsDictionary;
         private IEnumerable<PreValue> _preValuesAsArray;
@@ -82,5 +82,21 @@ namespace Umbraco.Core.Models
             }
             return result;
         }
+
+        public object DeepClone()
+        {
+            var clone = (PreValueCollection) MemberwiseClone();
+            if (_preValuesAsArray != null)
+            {
+                clone._preValuesAsArray = _preValuesAsArray.Select(x => (PreValue)x.DeepClone()).ToArray();    
+            }
+            if (_preValuesAsDictionary != null)
+            {
+                clone._preValuesAsDictionary = _preValuesAsDictionary.ToDictionary(x => x.Key, x => (PreValue)x.Value.DeepClone());    
+            }
+            
+
+            return clone;
+        }
     }
 }