Exchange account based invitations appear a second time in iCloud.

Hello,

When I receive an invitation on my PC at work and use my work email account (Microsoft Exchange) to respond to it, I always have a second (unresponded) invitation waiting for me on my Mac when I get home. How can I configure iCloud/iCal to understand that the invitation has been responded to in Microsoft Exchange?

I should add that my Exchange account is synced with iCal, and that there is always an accepted version of the invitation associated with the Exchange account in already there. I'd simply like to remove the second invitation that automatically shows up associated with my iCloud-based iCal calendar.

Thanks!