There were a few 158s on Nottingham Eastcroft yesterday (more than usual for that time) so they may be having a few problems. I've seen a lot of 156s on Skegness runs recently too, and most of these are (or at least were, and i've not heard of any changes) booked 158. 156401 also visited Liverpool yesterday on the 0640 from Nottingham, but it was paired with 158799 and detached at Nottingham on the return journey.