Installed the latest version of nidas (revision 5771M) today, with the new process running at 19:49 UTC.
The new nidas has some improvements in the serial handling efficiency. Don't see any effect on the number of "spurious interrupts" though.
Also restarted ntp daemon. Added a "server ral" entry in /etc/ntp.conf so that we can compare our local GPS time source with the ral server.