Status does not change

OK, so what I have here...:

- created one custom status, so now I have: unassigned, open, on hold & closed, resolved
- unassigned is the best status for me from which ticket should start, so I have set it up as a default status of a new ticket

I create (or someone else does) a new ticket, that is not assigned to anyone. As soon as this ticket is picked-up or assigned, my idea is, that the status changes to Open. But it does not. Also when the technician is assigned when the ticket is created, same scenario - the status remains unassigned.

Maybe I am missing something - perhaps creating custom status and using it as default for new ticket isn't the best advise?

Thanks for any feedback.