Okay, I have been following this thread and I am confident mine is doing a similarly weird thing.
Before I read this I always used to leave it in Sport and did sometimes feel like it wasn't actually in Sport apart from the additional noise. Then after reading this I started testing by putting it back into Normal then to Sport. As you have mentioned, I can certainly feel the difference and it does feel like it is actually in Sport mode.
I don't know if it is just a placebo effect, that when we physically switch over to Sport mode within that same journey we are just believing it is responding a little quicker? Don't know, but even after deliberately starting off in Sport, doing the switch to Normal and back again, noticing the difference and then switching engine off, then start up again whilst still in Sport, I am positive there it feels like its back in Normal mode, until I do the switchy thing again.
Such a strange issue...really interested to see what VW say adekil.