[Xymon] alerts.cfg DURATION rule being ignored

Hello,

Our Xymon server is monitoring about a hundred hosts and has been doing so nicely for years.? However DURATION rule is being ignored. I have several lines like this in alerts.cfg:

SCRIPT <script location> <email address> SERVICE=replication DURATION>30m REPEAT=30d COLOR=red,purple

Replication is a custom check. But the alert (scripted email) is being sent as soon as the check goes red, not 30 minutes later. Any suggestions as to why this could be? Using Xymon 4.3.30.