jQuery Grid Plugin - jqGrid

I have a jqgrid instance which posts an array of ids to the server. I would like the pass in a new list when an event is triggered. Instead of overwriting the old list, jqgrid will add to it. How can i set the post parameters to create a new list each time I reload the grid.

This is the code to reload the grid with new post data

  $('#gridConfirm').jqGrid('setGridParam',{postData:{'deviceIDs':$("#device").val()}});
  $('#gridConfirm').trigger('reloadGrid');

I've confirmed that $("#device").val() returns a list of id's in the form "5,6,7,8"; So i'm expecting this list to be posted to the server.

Instead, its posting "5,6,7,8" plus the previous list. so if the previous list was "1,2,3,4". It's posting "5,6,7,8,1,2,3,4"

How can i clear the previous posted list when reloading the grid?