There are a few extension methods added to IObjectSpace to help when working with multiple IObjectSpaceProviders. You typically only need this in advanced scenarios involving non-persistent objects.
IObjectSpace space = Application.CreateObjectSpace(typeof(MyNonPersistentObject));
if (space.IsNonPersistent())
{
IObjectSpace persistentspace = space.ForType();
//Work with the correct IObjectSpace now
}