clean up when detaching caption buttons and templates change.

src/Avalonia.Controls/Chrome/CaptionButtons.cs

@@ -38,12 +38,10 @@ namespace Avalonia.Controls.Chrome
         {
             if (_disposables != null)
             {
-                var layer = ChromeOverlayLayer.GetOverlayLayer(_hostWindow);
-
-                layer?.Children.Remove(this);
-
                 _disposables.Dispose();
                 _disposables = null;
+
+                _hostWindow = null;
             }
         }
 

src/Avalonia.Controls/Chrome/TitleBar.cs

@@ -42,6 +42,8 @@ namespace Avalonia.Controls.Chrome
         {
             base.OnApplyTemplate(e);
 
+            _captionButtons?.Detach();
+            
             _captionButtons = e.NameScope.Get<CaptionButtons>("PART_CaptionButtons");
 
             if (VisualRoot is Window window)
@@ -87,6 +89,9 @@ namespace Avalonia.Controls.Chrome
             base.OnDetachedFromVisualTree(e);
 
             _disposables?.Dispose();
+            
+            _captionButtons?.Detach();
+            _captionButtons = null;
         }
     }
 }