After changing assignee the changed assignee should be displayed in involve people.
1) Login with email@example.com/admin
1) Create task without assignee .It goes to 'My task'
2) Change the assignee to some other user (i.e Jenni Joy) .
3) Go to involved task and change again to some othe user (i.e Mike Hunt) and open the info-drawer
In the Involve people the 'administartor & Jenni Joy' name should be displayed
In the Involve people the 'administartor' name only is displayed