Google calendar duplicate entires

We use Google calendar shared between my iPhone 5 and and an Android phone. Most of the calendar events were entered on a PC, of which a great deal of them are repeating events. When I edit a repeating event on the PC or the Android phone it correctly edits the event, either just that one event or all future, or all in the series etc. When we edit the an event on the iPhone, it appears to work, but the calendar then displays duplicates of the edited event. Usually it will show up between 2 and 6 times per day. These don't just show on the iPhone, but they actually get created on the calendar and can be seen on a PC and the Android phone. We use calDAV for the connection to Google calendar, and it is the only calendar that is setup and/or displayed on the phone. I have seen people say stuff about the birthday calendar showing dupes, but have not seen anything quite like this.