Here is my fix:
Code:
if (isset($posted) && strlen(trim($tariffplan)) > 0){
$idtariff = explode('-:-',$tariffplan);
$HD_Form->FG_TOP_FILTER_NAME = str_replace ("-:-","",$idtariff[1]);
$HD_Form->FG_TOP_FILTER_VALUE = $idtariff[0];
$_SESSION["mytariff_id"] = $idtariff[0];
$HD_Form -> FG_TABLE_CLAUSE .= "cc_tariffplan.id = cc_tariffgroup_plan.idtariffplan AND cc_tariffgroup_plan.idtariffgroup = '".$_SESSION["tariff"]."' AND cc_tariffgroup_plan.idtariffplan=cc_ratecard.idtariffplan AND cc_ratecard.idtariffplan='".$HD_Form->FG_TOP_FILTER_VALUE."' AND cc_tariffgroup_plan.idtariffgroup = '".$_SESSION["tariff"]."'";
$_SESSION['def_ratecard'] = $HD_Form -> FG_TABLE_CLAUSE;
}else{
$HD_Form -> FG_TOP_FILTER_NAME = 0;
$HD_Form -> FG_TABLE_CLAUSE = "cc_tariffplan.id = cc_tariffgroup_plan.idtariffplan AND cc_tariffgroup_plan.idtariffgroup = '".$_SESSION["tariff"]."' AND cc_tariffgroup_plan.idtariffplan=cc_ratecard.idtariffplan AND cc_ratecard.idtariffplan='".$_SESSION["mytariff_id"]."' AND cc_tariffgroup_plan.idtariffgroup = '".$_SESSION["tariff"]."'";
}
PS You should edit carduser/form_data/FG_var_ratecard.inc