Don't deselect sibling item on PointerLeave.

src/Avalonia.Controls/Platform/DefaultMenuInteractionHandler.cs

@@ -301,17 +301,20 @@ namespace Avalonia.Controls.Platform
                 return;
             }
 
-            if (item.IsTopLevel)
+            if (item.Parent.SelectedItem == item)
             {
-                if (!((IMenu)item.Parent).IsOpen && item.Parent.SelectedItem == item)
+                if (item.IsTopLevel)
+                {
+                    if (!((IMenu)item.Parent).IsOpen)
+                    {
+                        item.Parent.SelectedItem = null;
+                    }
+                }
+                else if (!item.HasSubMenu)
                 {
                     item.Parent.SelectedItem = null;
                 }
             }
-            else if (!item.HasSubMenu)
-            {
-                item.Parent.SelectedItem = null;
-            }
         }
 
         protected internal virtual void PointerPressed(object sender, PointerPressedEventArgs e)

tests/Avalonia.Controls.UnitTests/Platform/DefaultMenuInteractionHandlerTests.cs

@@ -371,12 +371,30 @@ namespace Avalonia.Controls.UnitTests.Platform
                 var item = Mock.Of<IMenuItem>(x => x.Parent == parentItem);
                 var e = new PointerEventArgs { RoutedEvent = MenuItem.PointerLeaveItemEvent, Source = item };
 
+                Mock.Get(parentItem).SetupGet(x => x.SelectedItem).Returns(item);
                 target.PointerLeave(item, e);
 
                 Mock.Get(parentItem).VerifySet(x => x.SelectedItem = null);
                 Assert.False(e.Handled);
             }
 
+            [Fact]
+            public void PointerLeave_Doesnt_Deselect_Sibling()
+            {
+                var target = new DefaultMenuInteractionHandler();
+                var menu = Mock.Of<IMenu>();
+                var parentItem = Mock.Of<IMenuItem>(x => x.IsTopLevel == true && x.HasSubMenu == true && x.Parent == menu);
+                var item = Mock.Of<IMenuItem>(x => x.Parent == parentItem);
+                var sibling = Mock.Of<IMenuItem>(x => x.Parent == parentItem);
+                var e = new PointerEventArgs { RoutedEvent = MenuItem.PointerLeaveItemEvent, Source = item };
+
+                Mock.Get(parentItem).SetupGet(x => x.SelectedItem).Returns(sibling);
+                target.PointerLeave(item, e);
+
+                Mock.Get(parentItem).VerifySet(x => x.SelectedItem = null, Times.Never);
+                Assert.False(e.Handled);
+            }
+
             [Fact]
             public void PointerLeave_Doesnt_Deselect_Item_If_Pointer_Over_Submenu()
             {