Why is Thread.CurrentPrincipal not persisting after async await call

Question

I have the following code:

public async Task Get()
{
    // With .ConfigureAwait(false): "AspNetSynchronizationContext"
    // Without .ConfigureAwait(false): "AspNetSynchronizationContext"
    var synchContext = SynchronizationContext.Current.GetType().Name;

    // With .ConfigureAwait(false): "[email protected]"
    // Without .ConfigureAwait(false): "[email protected]"
    var originalName = Thread.CurrentPrincipal.Identity.Name;
    Thread.CurrentPrincipal = new CustomPrincipal("A");

    // With .ConfigureAwait(false): "A"
    // Without .ConfigureAwait(false): "A"
    var name = Thread.CurrentPrincipal.Identity.Name;

    await Task.Delay(1000).ConfigureAwait(false);
    //await Task.Delay(1000);

    // With .ConfigureAwait(false): null
    // Without .ConfigureAwait(false): "AspNetSynchronizationContext"
    var newSynchContext = SynchronizationContext.Current?.GetType().Name;

    // With .ConfigureAwait(false): "A"
    // Without .ConfigureAwait(false): "[email protected]"
    var newName = Thread.CurrentPrincipal.Identity.Name;
}

I set Thread.CurrentPrincipal to new CustomPrincipal("A"), then if I call await Task.Delay(1000).ConfigureAwait(false), the value is persisted afterwards.

However, if I call Task.Delay(1000), the value is not persisted, and Thread.CurrentPrincipal still contains its original value.

This seems like the opposite of what should happen based on this answer:

ASP.NET uses its SynchronizationContext to set Thread.CurrentPrincipal.

I thought if you use .ConfigureAwait(false), the original context is not put back, which I thought would have contained the original Thread.CurrentPrincipal.

Is Thread.CurrentPrincipal linked to the synchronization context? If so, why is the value that I set for it not persisted when I return to the original context?

Update:

I have <httpRuntime targetFramework="4.5" requestValidationMode="4.5" enableVersionHeader="false" />, and <compilation targetFramework="4.5.2" debug="true"> set in web.config.

However, <TargetFrameworkVersion>v4.7.2</TargetFrameworkVersion> is set in .csproj.