I've recently acquired a Hornby B1 and am duly impressed by its quality. However, when test running it with a rake of Hornby Gresley coaches, there is a tendency for the leading bogie of the first coach to derail. Close inspection shows that there is a small but definite height difference between the tender coupling and that of the coach. The tender lifts the coach and, despite the fact that the coach coupling is attached to the floor and not the bogie, there is enough lift to cause the flanges on the leading wheelset to ride over the top of the rail, epsecially when exiting from a curve. Has anyone else experienced this?