Server Sorting Makes Repeated call

I am using this demo for grid server sorting and i found the below issue.

https://dojo.telerik.com/uHAnIqoN

Steps to discover the issue:
1.Open the above link
2.Load the page
3.Hit Run
4.Open Developer Tool
5.Switch to the Network tab and filter by All 
6.Click Unit Price to sort. There is only one AJAX call.
7.Scroll to load the next page
8.Now click Units in stock to sort. It made two AJAX calls
9.First call doesn't contain the details of sortable column name and order of the column
10.Second call contain the details of sortable column name and order of the column

I dont know why it makes two AJAX calls.