Delay in sending lesson_status update, showing completion with FF

We're having an issue getting course completions to record properly.  We have courses that the user goes through, and then (typically) a brief quiz to verify that they learned the material, and with a passing score (again, typically 80% or higher), they get to a "congratulations, you passed!" screen.  They are then instructed to close the course window.  Upon doing so, the course remains in an "In Progress" state.

We captured the session data, and we see the status get set to In Progress when they first open the course.  After reaching the "Congrats" page, sometimes another lesson_status is sent, setting the status to P, upon that page loading.  Sometimes that last status update doesn't happen before the window is closed.  If we wait long enough on that last page (we've seen up to a 10 minute delay, so far), the lesson_status update gets sent.

We're posting our content using AICC, the courses are hosted on our internal server, and then we go to our LMS provider for tracking (and we were told AICC handles the split domains better).  The clients are running Firefox 3.5.8 on SuSE Linux.

Any suggestions?

Thanks.