If you can do the same maneuver in SD and not experience the lag - then it's a software problem (poor software design). But it also might be a matter of degree. The idea that it is "doing what it is designed to do" is a poor excuse that is too often offered when there is nothing wrong with your particular vehicle and "they all do that." The natural and often overlooked conclusion is that "...then they are all defective by design." With poorly designed software, that's what it often comes down to.
I have demonstrated to my tech that I get a 2 second lag when stepping on it as I coast down to 20mph. He readily agreed that it was an issue. My approach is that it is a safety issue (which it seriously is) and I have been presenting it this way. I'll be back in there in 2 weeks. As per BMWNA, the dealer will be working with BMW engineering on it. I think they can tell that I am unwilling to live with it as it is, and I would suggest that nobody should.
2012 535ix Space Gray, Cinnamon, SAT, Premium, Prem sound, Cold W., Sunshades, Gloss Black Grille, Gloss Black Side Markers, RE970AS 245/45/19 non-run flats that run very smooth + quiet and also correct the otherwise optimistic speedo