Pagination JqGrid Virtual Scroll

I have the following problem. I am using jqGrid with jquery with the following configuration and I try to implement the virtual scroll scroll: 1 .

var jqGridOptions = { url:'/index.php/solicitudes/DataSolicitudes',
  mtype : "post", 
  datatype: "json",
  colNames:['Id Solicitud','Contenido','Medio Respuesta','Ingreso','Fecha límite','Fecha Límite Completar','Estatus','Id_Estatus','Fecha Venc. Prorroga',"Nombre Unidad"],
  colModel:[
     {name:'id_solicitud',index:'id_solicitud', width: 80},
     {name:'contenido',index:'contenido', width: 400},        
     {name:'id_medio_respuesta',index:'id_medio_respuesta', width:120 },                              
     {name:'fecha_ingreso',index:'fecha_ingreso', width:90 },
     {name:'fecha_limite_entrega',index:'fecha_limite_entrega', width:90 },                          
     {name:'fecha_limite_completar',index:'fecha_limite_completar', width:150 },  
     {name:'id_estatus',index:'id_estatus', width:90 },         
     {name:'id_estatus2',index:'id_estatus2', width:20 },
     {name:'fecha_prorroga',index:'fecha_prorroga', width:140 },                           
     {name:'nombre_unidad_enlace',index:'nombre_unidad_enlace', width:250 }
  ],
  rowNum:50,
  autowidth: true,
  height:450,
  rowList:[50,100,200],
  pager: '#pagerSolicitudes',
  sortname: 'id_solicitud',
  viewrecords: true,
  sortorder: "desc",
  toolbar: [true,"top"],
  multiselect: false,
  shrinkToFit: false,
  gridview:true,
  scroll: 1,
  caption:"Solicitudes"
  };

 $solicitudes.jqGrid(jqGridOptions);

The problem is that when you scroll down, the next page is 4 and not 2, the next one is 8 and not 3. I have read and understand that it is a bug of the library itself, but is there any Solution for this ?, and download the latest version of the library 5.1.0, but I still does not work.

On the server side I use php.