Set rows with larger height value.
<style type="text/css">
.datagrid-row{
height:35px;
}
</style>
Or call 'fixRowHeight' method after the linkbutton is created.
onLoadSuccess: function(data){
//create the grid buttons
$(this).datagrid('getPanel').find('a.gridButtons').linkbutton();
$(this).datagrid('fixRowHeight');
}