See if I can explain myself properly:

A teacher created a recursive event that propagated on many consecutive days in our calendar. He created it as a site (or global) event. 

Later on, we decided it was better for it to be designated as "course" event, so we changed the type of event to course and for a while it worked. 

But a few hours (perhaps a day) the event had returned, actually added as another event altogether, and now we have two repeated events, one as global and one as course specific. 

Any ideas on why this would be happening and how to stop it? Even if it has some development implications, I would be interesting to follow the lead. 

Thanks!