Update TabControl on container index change.

src/Avalonia.Controls/Presenters/PanelContainerGenerator.cs

@@ -96,7 +96,7 @@ namespace Avalonia.Controls.Presenters
                 var childCount = children.Count;
 
                 for (var i = index; i < childCount; ++i)
-                    generator.ItemContainerIndexChanged(children[i], i - count, i);
+                    generator.ItemContainerIndexChanged(children[i], i + count, i);
             }
 
             switch (e.Action)

src/Avalonia.Controls/TabControl.cs

@@ -174,6 +174,16 @@ namespace Avalonia.Controls
             UpdateSelectedContent();
         }
 
+        protected override void ContainerIndexChangedOverride(Control container, int oldIndex, int newIndex)
+        {
+            base.ContainerIndexChangedOverride(container, oldIndex, newIndex);
+
+            var selectedIndex = SelectedIndex;
+            
+            if (selectedIndex == oldIndex || selectedIndex == newIndex)
+                UpdateSelectedContent();
+        }
+
         protected internal override void ClearContainerForItemOverride(Control element)
         {
             base.ClearContainerForItemOverride(element);