Well, I've had mine back too, and the bogie issue is all sorted - C-shaped spacers have been added to the bogie shaft. However, with no vertical movement between the couplings, and with the small gradient changes on my track, I still have derailment issues. I could run the power car and various combinations of 1, 2 and 3 carriages/dummy car without problems, but never managed a complete circuit of the track with 4 or 5 carriages. And never with the power car at the rear pushing forward in any combination. It was also pretty horrible crossing points. I tried loosening the couplings with a small turn of the retaining screw, but that didn't sort it either.
Sadly, I've decided to return to Hornby for a refund.