How reproducible:
Export an ical or vcal file from korganizer. mail it to a windows machine, 
click on the attachment andsave it. Open Outlook, select File->import and 
select vcal or ical (whichever is appropriate) and select that saved vcal or 
ical. Outlook will try to import it and fail.

Additional info:
I never complained about this before, but this bug exists for at least a year, 
if not two. It is present in different versions of Outlook.