take into account the extended mode when Resize is called.

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -483,8 +483,8 @@ namespace Avalonia.Win32
                     IntPtr.Zero,
                     0,
                     0,
-                    requestedClientWidth + (windowRect.Width - clientRect.Width),
-                    requestedClientHeight + (windowRect.Height - clientRect.Height),
+                    requestedClientWidth + (_isClientAreaExtended ? 0 : windowRect.Width - clientRect.Width),
+                    requestedClientHeight + (_isClientAreaExtended ? 0 : windowRect.Height - clientRect.Height),
                     SetWindowPosFlags.SWP_RESIZE);
             }
         }