Writing 4-channel m4a files wrong

If I try to output a 4-channel montage to an m4a file, whether aac-lc or aac-he, the result is a two-channel file.

In 9.5 this worked using aac-he but not aac-lc, and I reported it:
https://www.steinberg.net/forums/viewtopic.php?f=244&t=164024&p=878749&hilit=aac+lc+pwhodges#p878749
but now aac-he fails as well, so it’s worse…

Paul