Hi Jeronimo,
What is your EXOS version?
Please take a look at this command and its completion:
configure vlan untagged-ports auto-moveIt might be set to 'on' and I thing thats the case.
It might be set to informational or turned off, the latter will induce an error when you try to move a port untagged from one VLAN to another VLAN as untagged.
There is no such thing as moving ports between VLANs when they are tagged, as port can be a member of many VLANs when tagged. I doubt should it ask you "are you sure", as you're the expert to know what's going on. And an output that is exactly the same what you have issued in CLI is not useful at all - it doesn't make sure you're on the correct switch, that you will be sure of when phones begin to call. 😉
On the other hand, feature like commit/rollback would be awesome.
HTH,
Tomasz