vt7.3 - Listview sorting by related record field does not work

Tested and verified on demo.vtiger.com

Create a 2x Contacts related to 2x different Organisations, and give each Organisation different phone numbers (happens on any field though) In Contacts List view add the related organisations phone number as a field to be displayed. Sort the List by the Phone Number field. Then sort it again, and you'll see the order does not change.

It appears that it fails in /modules/Vtiger/models/ListView.php function getListViewEntries() line 209

$orderBy = $this->getForSql('orderby');

This returns false instead of the orderby column.