KOrganizer: deleted events appear again

Hi there,

I use KDE 4.3.5 and see this behaviour: if I delete an event in KOrganizer, 
the next time I start Kontact, this very event appears again...

I configured KOrganizer to use a folder where each calendar event is stored in 
its very own file. I can see when deleting an event, the files does not get 
deleted, it stays in the folder.

Why does KOrganizer not definitely delete the event? 

Regards
Malte