Don't notify AvaloniaProperty.Changed on non-effective value change.

src/Avalonia.Base/AvaloniaObject.cs

@@ -769,7 +769,11 @@ namespace Avalonia
             try
             {
                 OnPropertyChangedCore(change);
-                change.Property.NotifyChanged(change);
+
+                if (change.IsEffectiveValueChange && !change.IsOutdated)
+                {
+                    change.Property.NotifyChanged(change);
+                }
 
                 if (_listeners is object && _listeners.TryGetValue(change.Property, out var listener))
                 {

src/Avalonia.Base/AvaloniaPropertyChangedEventArgs.cs

@@ -80,7 +80,7 @@ namespace Avalonia
         public bool IsOutdated { get; private set; }
 
         internal void MarkOutdated() => IsOutdated = true;
-        internal void MarkInactiveValue() => IsEffectiveValueChange = false;
+        internal void MarkNonEffectiveValue() => IsEffectiveValueChange = false;
         protected abstract AvaloniaProperty GetProperty();
         protected abstract object? GetOldValue();
         protected abstract object? GetNewValue();

src/Avalonia.Base/PropertyStore/PriorityValue.cs

@@ -250,7 +250,7 @@ namespace Avalonia.PropertyStore
             }
             else if (change is object)
             {
-                change.MarkInactiveValue();
+                change.MarkNonEffectiveValue();
                 change.SetOldValue(default);
                 _sink.ValueChanged(change);
             }

tests/Avalonia.Base.UnitTests/AvaloniaPropertyTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Avalonia.Data;
 using Avalonia.Utilities;
 using Xunit;
@@ -88,6 +89,19 @@ namespace Avalonia.Base.UnitTests
             Assert.Equal("newvalue", value);
         }
 
+        [Fact]
+        public void Changed_Observable_Fired_Only_On_Effective_Value_Change()
+        {
+            var target = new Class1();
+            var result = new List<string>();
+
+            Class1.FooProperty.Changed.Subscribe(x => result.Add((string)x.NewValue));
+            target.SetValue(Class1.FooProperty, "animated", BindingPriority.Animation);
+            target.SetValue(Class1.FooProperty, "local");
+
+            Assert.Equal(new[] { "animated" }, result);
+        }
+
         [Fact]
         public void Property_Equals_Should_Handle_Null()
         {