I prepared a simple Dojo demo using your JSON and noticed that the agenda displays one additional task on 21st, which seems incorrect. I logged the issue for further investigation. The fix is scheduled for the next service pack of Kendo UI due the mid of February.
For now, you will need to continue using the agenda as it is, because there is no feasible workaround for this behavior.
As a gratitude for your involvement I updated your Telerik points.
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