[inflight regression] Fix Shell UI tests are failing in Candidate PR

src/Controls/src/Core/Shell/Shell.cs

@@ -397,6 +397,27 @@ internal static BackButtonBehavior GetEffectiveBackButtonBehavior(BindableObject
 		/// <param name="value">The View to be displayed in the navigation bar.</param>
 		public static void SetTitleView(BindableObject obj, View value) => obj.SetValue(TitleViewProperty, value);
 
+		// Determines whether the Shell's Title was set by the user (explicit code, style, or a binding)
+		// as opposed to being mirrored from the current page by the renderer (FromHandler) or never set
+		// at all (DefaultValue). This lets ShellToolbar mirror the page title into Shell.Title for
+		// TitleView bindings without clobbering a title the user set intentionally.
+		internal bool IsTitleSetByUser()
+		{
+			if (GetIsBound(TitleProperty))
+				return true;
+
+			var context = GetContext(TitleProperty);
+			if (context is null)
+				return false;
+
+			var specificity = context.Values.GetSpecificity();
+			return specificity != SetterSpecificity.DefaultValue && specificity != SetterSpecificity.FromHandler;
+		}
+
+		// Returns the Title only when it was set by the user. Used by the native window title
+		// fallback so that a renderer-mirrored page title never leaks into the platform chrome.
+		internal string GetUserSetTitle() => IsTitleSetByUser() ? Title : null;
+
 		static void OnFlyoutBehaviorChanged(BindableObject bindable, object oldValue, object newValue)
 		{
 			var element = (Element)bindable;

src/Controls/src/Core/ShellToolbar.cs

@@ -170,16 +170,18 @@ internal void UpdateTitle()
 				Shell.GetTitleView(_shell));
 
 			var title = GetCurrentTitle();
-			if (!IsShellTitleSetByUser())
-				_shell.SetValueFromRenderer(Shell.TitleProperty, title);
 
-			if (TitleView != null)
-			{
-				Title = String.Empty;
-				return;
-			}
-
-			Title = title;
+			// Mirror the current page's title into Shell.Title so that bindings inside a custom
+			// TitleView (e.g. {Binding Title, Source={x:Reference shell}}) can resolve to it.
+			// Use SetValueFromRenderer (FromHandler specificity) so the value is recognized as
+			// renderer-generated and does not leak into the native window title (see Window.cs),
+			// and only when the user hasn't explicitly set Shell.Title themselves.
+			if (!_shell.IsTitleSetByUser())
+				_shell.SetValueFromRenderer(Page.TitleProperty, title);
+
+			// The native nav-bar title must be empty when a custom TitleView is present,
+			// otherwise it should reflect the current page title.
+			Title = TitleView != null ? String.Empty : title;
 		}
 
 		string GetCurrentTitle()
@@ -198,18 +200,5 @@ string GetCurrentTitle()
 
 			return String.Empty;
 		}
-
-		bool IsShellTitleSetByUser()
-		{
-			var titleContext = _shell.GetContext(Shell.TitleProperty);
-			if (titleContext == null)
-				return false;
-
-			if (titleContext.Bindings.Count > 0)
-				return true;
-
-			var specificity = titleContext.Values.GetSpecificity();
-			return specificity != SetterSpecificity.DefaultValue && specificity != SetterSpecificity.FromHandler;
-		}
 	}
 }

src/Controls/src/Core/Window/Window.cs

@@ -131,7 +131,7 @@ public bool IsActivated
 			private set => SetValue(IsActivatedPropertyKey, value);
 		}
 
-		string? ITitledElement.Title => Title ?? (Page as Shell)?.Title;
+		string? ITitledElement.Title => Title ?? (Page as Shell)?.GetUserSetTitle();
 
 		public Page? Page
 		{

src/Controls/tests/Core.UnitTests/ShellToolbarTests.cs

@@ -302,6 +302,37 @@ public void ShellTitleReflectsCurrentPageTitleForTitleViewBindings()
 			Assert.Equal("Updated Test Title", label.Text);
 		}
 
+		// Regression test for https://github.com/dotnet/maui/issues/36562
+		// PR #35800 made ShellToolbar mirror the current page's title into Shell.Title (via
+		// SetValueFromRenderer) so TitleView bindings like {Binding Title, Source={x:Reference Shell}}
+		// resolve correctly. That mirrored value leaked into the native window title
+		// (ITitledElement.Title), which previously stayed empty in this scenario, breaking Shell UI
+		// tests around title/flyout layout on macOS/Windows.
+		[Fact]
+		public void WindowNativeTitleDoesNotLeakToolbarMirroredPageTitle()
+		{
+			var contentPage = new ContentPage() { Title = "Test Title" };
+			var titleView = new VerticalStackLayout();
+
+			TestShell testShell = new TestShell(contentPage);
+			var window = new Window()
+			{
+				Page = testShell
+			};
+
+			Shell.SetTitleView(contentPage, titleView);
+
+			// Shell.Title is mirrored from the page for TitleView binding purposes...
+			Assert.Equal("Test Title", testShell.Title);
+
+			// ...but that mirrored value must NOT leak into the native window title fallback.
+			Assert.Null(((ITitledElement)window).Title);
+
+			contentPage.Title = "Updated Test Title";
+			Assert.Equal("Updated Test Title", testShell.Title);
+			Assert.Null(((ITitledElement)window).Title);
+		}
+
 		[Fact]
 		public void ShellTitleBindingIsNotOverwrittenByCurrentPageTitle()
 		{