Datatables postgres duplicate rows paging

I'm using datatables plugin with postgres database. When I'm ordering columns I'm getting duplicate rows on some pages. For example:

When I'm sorting column "ASG" on first page:

And on the second page:

But when I'm sorting by Domain name (first column) everything is ok. Any ideas?

Here's my ssp.class file: https://github.com/guillermovil/datatables-postgres/blob/master/ssp.class.pg.php