I think I solved the problem. I ran pkgtool>Setup>services again and enabled rc.syslog (the Linux system logging utilities). Up to now, I do not see those strange messages, so the problem seems to be solved. Within /etc/rc.d/rc.syslog I read:
echo "/usr/sbin/klogd -c 3 -x"
# '-c 3' = display level 'error' or higher messages on console
# '-x' = turn off broken EIP translation
/usr/sbin/klogd -c 3 -x
So I expect that level 3 or greater errors will be displayed on console, but this ought to happen much less often and besides it would be good to know that there has been an important error.
One place where the messages invariably appeared was when booting and at system shutdown. Now I do not see them anymore.