Sort by "read" status does not work

I may be missing something, but whenever I click on the column header, I expect the email list to be sorted by the column being clicked, and each following click on the same column to invert the ordering.

This work nice with all columns, but seems to be ineffective with the "read/(unread)" one: the list order never gets updated.
Is there something special with that peculiar column. W/o this feature, it is hard to find the unread email in email account with many emails.

Sorting works smoothly on other columns, even the Flags one.

MM 1.14 (5798 & 5814) / macOS 11.4 (20F71)

Thanks.