Kendo Grid Add new row doesn't work when sorting Descending

Kendo Grid Add new row doesn't work when sorting Descending

I am using Kendo UI Grid with sortable enabled, when one of the field is
sorted descending the Add new record button doesn't work (Editable:
"popup") the popup window doesn't open.
here is an example http://jsbin.com/IsobegI/2/edit?html,js,output
to reproduce open the example then click on any of the fields' titles to
sort descending and then click the Add new record button and it wont work,
then sort ascending and click the button again it will work.
thanks for helping