I initially imported a several pst file into a Outlook 2007 profile. These items then synced with Office 365 and the entries matched up between Outlook and Outlook Web.
It was after the sync that I realized that some of the entries weren't needed.
So I went into Outlook and deleted all Calendar entries. I have waited several hours and I can still see all of the unwanted entries in Outlook Web.
Outlook doesn't appear to be syncing and says that this folder is up to date.