That's a bug.
Please apply this patch ( add it after including pqgrid js file )
pq.cRenderHead.prototype.getRowClsStyleAttr=function(e){var t=this.that.headerCells.length,r="";return e==t-1?r="pq-grid-title-row":t==e&&(r="pq-grid-header-search-row"),[r,"",""]};