The first week of January is looking to be 2, not 1. What can be the explanation?
Please, see the video https://youtu.be/Ker4d-KY6ck
As You see, we have an issue with weekNumbers for calendar. Year starts from 2 even 3(it's known issue). Also weeks are repeated.
On video used next example http://dojo.telerik.com/oYijoR
Thank you for the information. This behavior should be fixed in our upcoming official release scheduled for the beginning of May.