Auto-assign technician and creating new request manually

Hi there,

We have issues when we set Technician Auto-Assign and creating new incident manually.
What happened was:

we have 2 technician and auto-assign was set up as the following:
Select Tech Auto Assign model
       Round Robin
Execute when a request is
       Created
Apply Tech Auto Assign while creating requests to
        All Requests
let's say the technician's names are John and Brian
when John create new request manually, with the status set as [Closed], sometimes it got assigned to Brian even though he explicitly set the technician as himself

Any idea?
Perhaps i should set the following settings?
Apply Tech Auto Assign while creating requests to
Unassigned Requests Only

Thank you for your advice.