> From my point of view, the problem is the unpredictable behavior of
> our LISTSERV when a sequence of
>
>    GET listname (HEADER
>    UNLOCK listname
>
> is sent by one of our list owners. At least one list owner has done this and
> got puzzled by the result.

In general, there's no guarantee that mail will arrive in the order
that it was sent or be processed by LISTSERV in the order it was
received.  So it's not good to depend on that.