[C] 2W bindings always apply

don't ask me why, that's how it is

- fixes #16849

src/Controls/src/Core/BindableObject.cs

@@ -211,7 +211,7 @@ public void RemoveBinding(BindableProperty property)
 
 		/// <include file="../../docs/Microsoft.Maui.Controls/BindableObject.xml" path="//Member[@MemberName='SetBinding']/Docs/*" />
 		public void SetBinding(BindableProperty targetProperty, BindingBase binding)
-			=> SetBinding(targetProperty, binding, SetterSpecificity.FromBinding);
+			=> SetBinding(targetProperty, binding, binding != null && targetProperty != null && binding.GetRealizedMode(targetProperty) == BindingMode.TwoWay ? SetterSpecificity.FromHandler : SetterSpecificity.FromBinding);
 
 		internal void SetBinding(BindableProperty targetProperty, BindingBase binding, SetterSpecificity specificity)
 		{

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

@@ -2308,5 +2308,35 @@ public void NullRefWithDefaultCtor()
 			var label = new Label();
 			label.SetBinding(Label.TextColorProperty, new Binding());
 		}
+
+		[Fact]
+		//https://github.com/dotnet/maui/issues/16849
+		public void ValueFromHandlerDoesntClearWayBinding()
+		{
+			var vm = new MockViewModel();
+			var entry = new Entry { BindingContext = vm};
+			entry.SetBinding(Entry.TextProperty, "Text", BindingMode.TwoWay);
+			entry.SetValueFromRenderer(Entry.TextProperty, "foo");
+			Assert.Equal("foo", vm.Text);
+			vm.Text = "bar";
+			Assert.Equal("bar", entry.Text);
+			vm.Text = string.Empty;
+			Assert.Equal(string.Empty, entry.Text);
+		}
+
+		[Fact]
+		//https://github.com/dotnet/maui/issues/16849
+		public void ManualValueDoesntClearWayBinding()
+		{
+			var vm = new MockViewModel();
+			var entry = new Entry { BindingContext = vm };
+			entry.SetBinding(Entry.TextProperty, "Text", BindingMode.TwoWay);
+			entry.SetValue(Entry.TextProperty, "foo");
+			Assert.Equal("foo", vm.Text);
+			vm.Text = "bar";
+			Assert.Equal("bar", entry.Text);
+			vm.Text = string.Empty;
+			Assert.Equal(string.Empty, entry.Text);
+		}
 	}
 }