There is an issue with the .k-sorted class being applied to the last column in the grid when the actual column is not visible. It also is not updating the k-sorted when a sort is applied after the grid was created. 

This seems to be an issue in the latest release if the column sorted on is hidden, the last column in the grid gets the class. I also noticed that sorting a column does not apply the k-sorted class to the correct column: https://dojo.telerik.com/@dojolee/eFIbaSUn