Balance 380 port based VLAN

I am a little bit confused. I can not select custom VLANs unter Port Configuration / Trunk. Only Any is available. Balance One, Balance 710 and a lot of MAX devices support custom VLAN selection under port type Trunk.
This is HW6 FW 8.1

Best Regards

I fired a ticket for this. For everybody else having the same problem - I will post the solution here later.