jQuery Grid Plugin – jqGrid

I have initialized a new grid with "multiselect" option set to true. After initializing the grid, I decide NOT to let the user choose multiple rows based on some input. I do this by

$( "table[id='" + namespace + "']" ).setGridParam({
multiselect:false
});

This removes all checkboxes in all rows but keeps the "Select All" checkbox on the header of the grid. The grid is NOT multiselect anymore but the "Select All" checkbox stands still.

The image below is a screenshot of what I am getting after changing the value of "multiselect"  to false.