Performance issue of sortable + bindings in a grid

Please have a look at this rudimentary version of a query builder that I aim to create.

http://dojo.telerik.com/uKeCe

Try out the sortable feature. I think you notice the time lag at row drop. Is there anything that could be optimized in the code to eliminate it? Am I doing anything wrong? ...I did not have the nerve to try it, say, on IE10 ;-)

Also, what should I do to have the binding cast null sortDir value as empty string, ie. '(none)'?

Best,

moniuch