Slightly glad in away to hear other people are having related issues... Did a bit of testing...
This shows me fathing about with the bogie... Probably not worth watching. You can see the sticky out bit on the bogie catches the other sticky out bit on the body shell. It disconnects the clips and then gets stuck. Fathing then commonsense to try and clip it back in on camera where it fixes for a bit. And then a comparison with the 395 on how lovely and free its bogie is.
Video of it derailing (quite minor in this case though)
Video of it running without bodies (derails much later)
Video if it running with out the dummy unit, doesn't derail at all. I think as this type of coupling is so rigid, it must have had effect from the dummy car which still had body on...
And in case anyone is interested, Gosh, this unit can get some serious speed up. Was very unexpected from this motor set up type from me! Bachmann add more speed please!!!
Would probably work properly if "the sticky out bit on the bogie" (or the bit on the body) was cut off. However, Hornby said to send it in so will be doing that - not sure what they will do however!
(And apologies if the music isn't to taste, I have ASDA FM playing from an internet radio as I have a model ASDA store which you may be able to spot in one or two of the videos - got to be accurate!)