WebCalendar: duplicate entries

I’m running calendar version 1.0.5, as hosted by Dreamhost. Every time someone edits and saves an existing calendar event, the event title appears twice. The only way I’ve found to get rid of the duplicate entry is to press the Edit button again, then press the Save button again. Each time someone presses the Edit and Save buttons (it doesn’t matter if they actually edit the text before they press the Save button), the title of that event alternates between appearing once and twice. Can you share with me a) why that’s happening in the first place, and b) how I can fix whatever is broken so that the duplicate entry title stops appearing whenever someone edits an existing event?