FWIW, the fix was to change the locking to FCNTL in the kmail accounts settings.
Just in case someone searches the history here for a similar problem.
This forum however, seems rather useless in that what might be a common problem for those who attempt to make kmail run smoothly by offloading the mail fetching and spam filtering to a fetchmail/procmail/spamassassin solution, thereby removing 95% of the background work it has to do, and which can result in the composer itself being frozen for the duration of such background work, to only a second or so's stutter while it pulls from and sorts those incoming messages from the users /var/spool/mail/username mailfile, to its own database.
To me, the improvement in just plain old usability is a very worthwhile result.
What this distribution really needs is a mailing list. This 'forum' format, where someone has to click on the subject to open the message, functionally denies 99% of the eyeballs here from ever seeing a plea for help, whereas a mailing list, being scanned at about 1 second per message intervals, will make me stop and back up to an interesting message because the first paragraph was subliminally interesting, and this effect alone would generate lots more answers, something my original message to this forum did not do in 6 days.