jQuery Grid Plugin - jqGrid

I am having an issue with resetting the search filter on a grid when the rowNum is set to -1. I have a loadonce grid that receives json data then works completely on the client side. Part of its functionality involves programmatically applying a filter to it. To apply the filter I wrote the following method:

function searchGrid(gridId, field, string) {

    var grid = $('#' + gridId);

    var postdata = grid.jqGrid('getGridParam', 'postData');

    $.extend(postdata,

        { filters: '',

           searchField: field,

           searchOper: 'eq',

           searchString: string

          });

   grid.jqGrid('setGridParam', { search: true, postData: postdata });

   grid.trigger("reloadGrid", [{ page: 1}]);

}

The function for clearing the filter on a grid is as follows:

 function resetGrid(grdName) {

 var grid = $('#' + grdName);

 grid.jqGrid('setGridParam', { search: false });

var postData = grid.jqGrid('getGridParam', 'postData');

$.extend(postData,{searchField:"",searchString:"",searchOper:""});

grid.trigger("reloadGrid", [{ page: 1}]);

When I set the rowNum option for the grid to a number, the above works as expected. When I set rowNum to -1, the grid initially contains all of the rows (as expected). But when I try to search the grid or reset it, it shows the correct rows but one is chopped off. For example, say the grid pull back 10 rows. Before I use either of  the above methods, the grid has 10 rows. If I call the reset method, the grid now has 9 rows (instead of 10). If I perform a search that should retrieve 1 result, the grid is empty (should show the 1 result).