$t.sortData(colname, idx, reload);

However sortData requires an index (in the form jqgh_ + colname) to be able to re-apply the sort image and correctly set the sortname.

Here is a snippet form the sortData code that relies on the index having 'jqgh_' as a prefix to the colname.

$("tr th div#jqgh_"+ls+" img",thd).remove();
$("tr th div#jqgh_"+ls,thd).parent().removeClass(ts.p.sortclass);
iId = index.replace('.',"\\\\.");
$("tr th div#"+iId,thd).append(imgs).parent().addClass(ts.p.sortclass);
ts.p.lastsort = idxcol;
index = index.substring(5);
ts.p.sortname = ts.p.colModel[idxcol].index || index;
so = ts.p.sortorder;
if(onSortCol) {onSortCol(index,idxcol,so);}

 You can see that the image is removed along with the class using an id of jqgh_ + a column name. However if the index passed into sortData does not have jqgh_ as a prefix (as it does when called from other parts of grid.base.js) the sorting does not work.

My fix to this has been to alter sortGrid function in grid.custom.js to the following:

sortGrid : function(colname,reload){
        return this.each(function(){
            var $t=this,idx=-1;
            if ( !$t.grid ) { return;}
            if ( !colname ) { colname = $t.p.sortname; }
            for ( var i=0;i<$t.p.colModel.length;i++ ) {
                if ( $t.p.colModel[i].index == colname || $t.p.colModel[i].name==colname ) {
                    idx = i;
                    break;
                }
            }
            if ( idx!=-1 ){
                var sort = $t.p.colModel[idx].sortable;
                if ( typeof sort !== 'boolean' ) { sort =  true; }
                if ( typeof reload !=='boolean' ) { reload = false; }
                /* David Gallop 5/3/2009
                 * The colname expected by the sortData function
                 * in grid_base.js requires a prefix of jqgh_
                 * as it is used as an id to the grid header
                 */
                if ( sort ) { $t.sortData('jqgh_' + colname, idx, reload); }
            }
        });
    },

Please could this fix be included in future releases.

best regards and keep up the good work, Dave.