I sync an iCal calendar feed to a WordPress site using the Upcoming Events Widget. I do this primarily because it is the only calendar widget available with the free version of WordPress this non-profit is using.
The issue I had is that I deleted an event last week, yet it still shows in my WordPress site through this sidebar widget. I would think it was a refresh issue, but edits to other events at the same time have already sync’d to the WordPress site.

I even tried deleting the Widget and adding a new one and the new widget also shows the events that I deleted.
I was beginning to get a bit frustrated and of course I had a band parents breathing down my neck questioning my ability to manage the band parent association website. Okay, not really, but they did point out the discrepancy on the calendar and I assumed that they just thought I was an idiot.
After a bit of Googling turned up nothing, it occurred to me that this was a reoccurring event. When I deleted that event, I simply delete that particular occurrence of the events, not the whole series of events.
Sure enough, after I deleted the whole series of recurring events the event disappeared from the Upcoming Events Sidebar widget about an hour later. Longs story short, the Upcoming Events Widget in WordPress does not handle exceptions to recurring events reliably.