Nerijus Baliunas writes:
I got an answer from balsa developers:
Could it be because courier uses \HasChildren and \HasNoChildren
instead of \Noinferiors?
I haven't checked this actually but I was told \HasChildren is not in
standard, it's covered by a draft only. Is it a production Courier IMAP
Is \HasChildren really only a draft?
Yes, because \NoInferiors is broken, and is obsolete.