Critical alerts page and acks

I am having a problem with the nkview page. "Acked" alerts do not disappear off the page, they stay on the Critical Systems page, without even a check mark to indicate that they have been acked. The check mark does show up on the normal page for that host and the acknowledgment text is displayed on the test page. Has anybody seen behavior like this, or have any idea what could be causing it?

Thanks, Larry Barber