never had that. I think your doing far too slow a change here and too purposefully, if momentarily the engine is not in gear then it might start to think it's slowing to a stop and start to shut down the injectors like when your stopping. When changing down I usually do a racing change, and fast, always have done, so all at the same time and give the pedal a good "BLIP" of revs. I will try some deliberate slow changes tommorrow and see what happens.
But what you describe is close to the other end of the spectrum here, others also report the same, mine does it. Cruising in gear and a sudden slowing of pace (traffic backing up) so off throttle for a split second, then back on and there is no immediate pick up, you have to prod the throttle to get pick up back, like the engine is switched off. Doesn't always do it but very noticeable when it does, MT say this is fine, probably again the ecu is a bit confused and wondering what to do for a split second.