@AudioTrack Thank you so much for taking the time to help me.

I found another workaround in addition to what you suggested. I can enter an Asus4/D and get the correct notes. Unfortunately, the arrangement and song setting, "Natural Arrangements" doesn't fix it.

Despite a workaround, surely this is a bug? In fact, if I open the chord builder and choose D2 I get exactly the same chord as if I chose D > other > add2.