Call it a pet peeve of whatever, but this is something that's been bugging for a long time. What is up with Henry's TV series tender? And more to the point, what is it?

It sort of resembles his original Railways series look, or looks rather, but after his rebuild he was drawn with the standard black-five tender. Does anyone here know if Henry's big block tender has a basis IRL, or was the production team just too lazy to build a new model-accurate one after his rebuild?