After the minor bug in the ADM authoring tool, I have discovered a second, more serious bug.
I need to make some quick changes to an Atmos project. As I only need to make one small change, I imported the ADM master file intended for use in the Dolby encoder.
I noticed that I could not select a renderer in the appropriate channel layout during import. In the import dialogue, the selection only goes up to 7.1.4. The 9.1.6 layout is missing.