Helpdesk: previous link between ticket and custommer persist even custommer is changed

[DlemireForOdoo]

Impacted versions: V14

Steps to reproduce:

1. helpdesk: create a ticket and link with customer 1
2. connect customer 1 to the portal and look ticket
3. Change the customer's ticket with customer 2
4. connect customer 2 to the portal and sees ticket
5. connect customer 1 to the portal and sees ticket
6. with timesheet registered , the two custommer look the ticket from portal

Current behavior:
customer 1 sees the customer 2 ticket

Expected behavior:
only the customer displayed on ticket view must see the ticket

Video/Screenshot link (optional):

Support ticket number submitted via odoo.com/help (optional):

[pedrobaeza]

As this is something enterprise, please report it through odoo.com/help instead.