Welcome aboard Tim!
What you described could happen in case the event's ID field is not updated. Basically, new events are created with ID = 0 (unless specified otherwise), then unique ID should be assigned on the server and sent back to the client. If the server does not return an objects with updated ID, then the Scheduler's DataSource will treat that event as new, despite that it was saved, so it will be removed when closing the edit popup. I would recommend checking this article
, as well as our offline examples, which are located in the Kendo UI installation path, under the \wrappers\aspnetmvc\Examples directory.
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