jQuery Grid Plugin - jqGrid

Hello everybody,

this is my situation:

i have 2 grid: library and songs.

I can drag a record from library grid and drop it to the tail of songs grid :

jQuery("#library").jqGrid('gridDnD',{connectWith:'#songs',droppos:"last"});

Now i would like to sort my records in songs grid dragging a row  and dropping it to the desidered position:

jQuery("#songs").jqGrid('sortableRows');

Til now everything it's ok, but (damn but!) when i drop the row in order to sort it, a copy of the same row appear.

How can i avoid this behaviour?