Ticket Transfer Doesn't work with Filters

[etessam]

osTicket (v1.9.15)

I've set filters to auto-assign received tickets. It work as designed, however when Transferring the ticket to another person, the ticket is still assigned to: the prev. staff in the Open Ticket view.
And when opening the ticket it shows: Perv. Staff/New StafforGroup.

I want to know the php file that displays this information in the Open Ticket view. Plus the php file for assigning tickets.