When clear="true" in the <auto-acknowledge> tag (notifd-configuration.xml) the
up notice that matches a previous down message and acknowledges it is not
propagated through the notification path up to the targets that have received
the first notice.

On the other hand, if clear="false" the first message is ack'ed but the second
message is not cleared, and is propagated up the escalation ladder if not
acknowleged by hand. So, in this case targets that did not receive the down
message receive up message...

As Bill Felling stated on the discuss list:
> The ideal behavior from my point of view would be that when the "up" notice
> comes in, if clear="true" is set it clears the down notice, is sent to as
> many people as received the "down" notice, and then clears itself.

I am not sure which of all the possible situation are the most usefull (or
needed at all), but I agree with Bill's "ideal behaviour".