Time Spent Calculation should auto pause where there is no activity at all for a period

When you try and report on the actual time spent by users on courses - often its ridiculous amounts shown like 300 hours - I think that people start a course, then go off and do something else, and it keeps counting the time until the course is manually ended. There should be an inactivity timeout - of say 5 pr 10 minutes - after which time the couter gets paused until there is a mouse click on the screen or something. Otherwise the statistics become invalid...