After editing a calendar even in a recurring series a duplicate title with a (1) or (2) is created in the list view; as the below image shows
The duplicate titles are intended functionality of the CMS. While the titles appear duplicate, the CMS identifies them by the "Event Type". It will show the original occurrence, the canceled (modified) occurrence, and the newly occurred occurrence. These duplicate titles should not have any effect on the front-facing (the website's) calendar.