In .NET, System.Threading.Thread.CurrentPrincipal isn't updating

I'm missing something elementary here when debugging some .NET code:

    public static void CreateServiceSessionStore()
    {
        ServiceSessionStore serviceSessionStore = new ServiceSessionStore();
        serviceSessionStore.SetIdentity(System.Threading.Thread.CurrentPrincipal.Identity);
        System.Threading.Thread.CurrentPrincipal = serviceSessionStore;
        // Here, CurrentPrincipal still isn't a serviceSessionStore!
    }

In this code, everything seems to chug merrily along. However...when I debug and am just before the last line, I'm looking at System.Threading.Thread.CurrentPrincipal. The value is a WebSessionStore object, which is what I expect, and what I am thinking the last line should change it to a ServiceSessionStore object. But it doesn't. I can look at serviceSessionStore, and it's holding a ServiceSessionStore object, but after the line runs CurrentPrincipal still contains a WebSessionStore object. No error is thrown.

Now, aside from what these objects actually do, can someone offer an idea about why it seems to be refusing to update CurrentPrincipal?

This is a debugger artifact. Debug expressions are evaluated on a dedicated debugger thread. CurrentPrincipal is a property of the thread's execution context. Also the reason it can be a static property. Different threads will have different principals and the debugger thread's principal is therefore not the same.

You don't have a real problem.