Separating Event Registrations and Donations: Duplicate donations appearing!

Last year, we configured our Event Registrations so that event registration fees and additional donations come through separately (not as split gift). Has worked perfectly!  Recently, we are seeing duplicate donations along with the event registration.  Donor's credit card is being charged properly (not getting charged twice) but the donation transaction is coming through as two identical gifts.   Has anyone seen this happen? Cause? Cure?  Thanks!!!