WPF AutomationProperties.LiveSetting="Polite" not triggering live region updates

[GeoffYin]

Description

I have an AccessText element with text that updates every second. I hope that each text update doesn't interrupt the previous reading by Narrator. However, when I set the property AutomationProperties.LiveSetting = "Polite", it still doesn't work. Narrator still interrupts the previous reading and starts reading the next text update. the version of dotnet framwork is 4.8

Reproduction Steps

1. Add an AccessText that updates once every second, and set the property AutomationProperties.LiveSetting = "Polite".
2. Turn on Narrator scan mode.
3. Use the arrow keys to make Narrator focus on the AccessText.

Expected behavior

The expected result is that after setting the AutomationProperties.LiveSetting = "Polite" property, Narrator should not interrupt the previous text reading, just like the aria - live="polite" property in HTML.

Actual behavior

Narrator interrupts the previous reading and starts reading the newly updated text even before finishing the previous one.

Regression?

No response

Known Workarounds

No response

Impact

No response

Configuration

No response

Other information

No response

[lindexi]

@GeoffYin Do you set Switch.UseLegacyAccessibilityFeatures?

wpf/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Automation/Peers/AutomationPeer.cs

Lines 2424 to 2427 in ee7cbb8

	if (!AccessibilitySwitches.UseNetFx47CompatibleAccessibilityFeatures && AutomationElementIdentifiers.LiveSettingProperty != null)
	{
	s_propertyInfo[AutomationElementIdentifiers.LiveSettingProperty.Id] = new GetProperty(GetLiveSetting);
	}

wpf/src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/AccessibilitySwitches.cs

Lines 46 to 65 in ee7cbb8

	#region UseNetFx47CompatibleAccessibilityFeatures
	internal const string UseLegacyAccessibilityFeaturesSwitchName = "Switch.UseLegacyAccessibilityFeatures";
	private static int _useLegacyAccessibilityFeatures;
	/// <summary>
	/// Switch to force accessibility to only use features compatible with .NET 47
	/// When true, all accessibility features are compatible with .NET 47
	/// When false, accessibility features added in .NET versions greater than 47 can be enabled.
	/// </summary>
	public static bool UseNetFx47CompatibleAccessibilityFeatures
	{
	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	get
	{
	return LocalAppContext.GetCachedSwitchValue(UseLegacyAccessibilityFeaturesSwitchName, ref _useLegacyAccessibilityFeatures);
	}
	}
	#endregion