@richard.hriech Meh, unfortunately you were right! I just tested it again thoroughly in a quiet room and it seems that as soon as you switch from the real ANC Indoor to, say, Transparency or Normal and then back to ANC, it will default back to Outdoor/Transport, while still showing Indoor as the selected mode. You can tell that by the HISS volume, which is slightly louder in Outdoor/Transport mode than the hiss in Indoor mode. Same thing when you turn OFF and then turn ON again the headphones. Although it will still show Indoor as the selected mode in the app as before I turned off the headphones, the hiss will actually be that of the Outdoor/Transport mode.
So it seems that as soon as you switch from ANC Indoor mode to Transparency/Normal or turn off the headphones, when you switch back to ANC (or turn on your headphones) it will again default to ANC Outdoor (or Transport for that matter) even though it appears as Indoor in the app.
As a result, you always have to manually switch inside the app to another ANC mode and then back to Indoor to really get the Indoor experience. Argh, really frustrating.