Version:           1.8.2 (using KDE KDE 3.4.2)
Installed from:    SuSE RPMs
Compiler:          n/a: packaged binary 

Subject says it. 

Note: This wishlist item is intended to follow up on the bug report 
entitled: "Filter logging is deactivated everytime KMail is restarted"

http://bugs.kde.org/show_bug.cgi?id=98765

In that report, Andreas Gungl states:

"The behavior is intended. So let's make it a wish."

This submission is to get this item on the wish list and to
allow those who support this change to state our case (and
those who don't to refute it).

Reason for change: I think the typical use case for this facility
is when a user observes that filters are not behaving as expected.
The log is turned on to help debug. At that moment, though, a user
typically cannot 'requeue' the messages that were not filtered as
expected; the user must wait for more. Since most messages arrive 
in the morning, for most users this means that a kmail restart is 
involved. But if the user does not remember to turn the filter log
back on before fetching mail, the opportunity to capture data is lost.

There is already a log size limiter in place, so disk space is
not an issue.

Final note: this need not be an either/or proposition. If users
want both behaviors, a subordinate checkbox labeled something
like "retain this setting next time kmail starts" could be added.