Incorrect score using Tin Can API when course resumed

Hi,

I would be grateful for any suggestions to resolve a scoring issue on a course I have changed to Tin Can LMS output rather than Scorm 1.2.  I needed to change the reporting API as the send data limit in Scorm 1.2 was causing the course to freeze when learners were closing & resuming the course.  

Now on testing the Tin Can course when closing the course & resuming in the LMS a few times,  the quiz results are not giving the correct calculation.  It is like they haven't been communicated before the course window is closed.  I have tested in Talent LMS & Scorm Cloud with the same result.  I have tested when the course window is not closed/course is not resumed & get completely accurate results.

Any ideas out there to solve this? Is it a Tin Can only issue?

Many thanks,
David