Fixes pretty big issue with MediaType's not implementing the same IsDirty property check rules as ContentType when they should have shared the same rules. After removing caching on the unit tests, this bug became known.

src/Umbraco.Core/Models/ContentType.cs

@@ -120,67 +120,7 @@ namespace Umbraco.Core.Models
 
             return result;
         }
-
-        /// <summary>
-        /// Indicates whether a specific property on the current <see cref="IContent"/> entity is dirty.
-        /// </summary>
-        /// <param name="propertyName">Name of the property to check</param>
-        /// <returns>True if Property is dirty, otherwise False</returns>
-        public override bool IsPropertyDirty(string propertyName)
-        {
-            bool existsInEntity = base.IsPropertyDirty(propertyName);
-
-            bool anyDirtyGroups = PropertyGroups.Any(x => x.IsPropertyDirty(propertyName));
-            bool anyDirtyTypes = PropertyTypes.Any(x => x.IsPropertyDirty(propertyName));
-
-            return existsInEntity || anyDirtyGroups || anyDirtyTypes;
-        }
-
-        /// <summary>
-        /// Indicates whether the current entity is dirty.
-        /// </summary>
-        /// <returns>True if entity is dirty, otherwise False</returns>
-        public override bool IsDirty()
-        {
-            bool dirtyEntity = base.IsDirty();
-
-            bool dirtyGroups = PropertyGroups.Any(x => x.IsDirty());
-            bool dirtyTypes = PropertyTypes.Any(x => x.IsDirty());
-
-            return dirtyEntity || dirtyGroups || dirtyTypes;
-        }
-
-        /// <summary>
-        /// Resets dirty properties by clearing the dictionary used to track changes.
-        /// </summary>
-        /// <remarks>
-        /// Please note that resetting the dirty properties could potentially
-        /// obstruct the saving of a new or updated entity.
-        /// </remarks>
-        public override void ResetDirtyProperties()
-        {
-            base.ResetDirtyProperties();
-
-            //loop through each property group to reset the property types
-            var propertiesReset = new List<int>();
-
-            foreach (var propertyGroup in PropertyGroups)
-            {
-                propertyGroup.ResetDirtyProperties();
-                foreach (var propertyType in propertyGroup.PropertyTypes)
-                {                    
-                    propertyType.ResetDirtyProperties();
-                    propertiesReset.Add(propertyType.Id);
-                }
-            }
-            //then loop through our property type collection since some might not exist on a property group
-            //but don't re-reset ones we've already done.
-            foreach (var propertyType in PropertyTypes.Where(x => propertiesReset.Contains(x.Id) == false))
-            {
-                propertyType.ResetDirtyProperties();
-            }
-        }
-
+        
         /// <summary>
         /// Creates a clone of the current entity
         /// </summary>

src/Umbraco.Core/Models/ContentTypeBase.cs

@@ -503,5 +503,65 @@ namespace Umbraco.Core.Models
         {
              get { return _propertyTypes; }
         }
+
+        /// <summary>
+        /// Indicates whether a specific property on the current <see cref="IContent"/> entity is dirty.
+        /// </summary>
+        /// <param name="propertyName">Name of the property to check</param>
+        /// <returns>True if Property is dirty, otherwise False</returns>
+        public override bool IsPropertyDirty(string propertyName)
+        {
+            bool existsInEntity = base.IsPropertyDirty(propertyName);
+
+            bool anyDirtyGroups = PropertyGroups.Any(x => x.IsPropertyDirty(propertyName));
+            bool anyDirtyTypes = PropertyTypes.Any(x => x.IsPropertyDirty(propertyName));
+
+            return existsInEntity || anyDirtyGroups || anyDirtyTypes;
+        }
+
+        /// <summary>
+        /// Indicates whether the current entity is dirty.
+        /// </summary>
+        /// <returns>True if entity is dirty, otherwise False</returns>
+        public override bool IsDirty()
+        {
+            bool dirtyEntity = base.IsDirty();
+
+            bool dirtyGroups = PropertyGroups.Any(x => x.IsDirty());
+            bool dirtyTypes = PropertyTypes.Any(x => x.IsDirty());
+
+            return dirtyEntity || dirtyGroups || dirtyTypes;
+        }
+
+        /// <summary>
+        /// Resets dirty properties by clearing the dictionary used to track changes.
+        /// </summary>
+        /// <remarks>
+        /// Please note that resetting the dirty properties could potentially
+        /// obstruct the saving of a new or updated entity.
+        /// </remarks>
+        public override void ResetDirtyProperties()
+        {
+            base.ResetDirtyProperties();
+
+            //loop through each property group to reset the property types
+            var propertiesReset = new List<int>();
+
+            foreach (var propertyGroup in PropertyGroups)
+            {
+                propertyGroup.ResetDirtyProperties();
+                foreach (var propertyType in propertyGroup.PropertyTypes)
+                {
+                    propertyType.ResetDirtyProperties();
+                    propertiesReset.Add(propertyType.Id);
+                }
+            }
+            //then loop through our property type collection since some might not exist on a property group
+            //but don't re-reset ones we've already done.
+            foreach (var propertyType in PropertyTypes.Where(x => propertiesReset.Contains(x.Id) == false))
+            {
+                propertyType.ResetDirtyProperties();
+            }
+        }
     }
 }