Possible bug in the Manage Employee Section

I have two different categories lets call them A and B and employees can work multiple assignments and able to view those assignments in "My working List"; provided that employee is selected in the select user field in the Manage employee section but for some reason that field will not let me select two identical users for project A and Project B only allowed me to select the same user name for one and not the other. Please investigate or advice on what I need to do to be able to view all my assigned appointments regadless of the category.
As you can see from the attachment, emp1 accepted the user name and emp2 did not.