NSHomeDirectory doesn't give sandboxed "Container" path even when sandboxed

According to Apple's documentation for NSHomeDirectory()...

In OS X, it is the application’s sandbox directory or the current user’s home directory (if the application is not in a sandbox)

However, even when I choose the option to "Enable App Sandboxing", a call to NSHomeDirectory() always returns /Users/{username} instead of /Users/{username}/Library/Containers/{bundleID}/Data. For NSHomeDirectory(), I'm currently using...

[DllImport(MonoMac.Constants.FoundationLibrary)]
public static extern IntPtr NSHomeDirectory();

public static string ContainerDirectory
{
    get {
        return ((NSString)Runtime.GetNSObject (NSHomeDirectory ())).ToString ();
    }
}

I've emailed Xamarin support which they "sent to the engineers", but they suggested I ask on here as well. Thoughts?