Some specific users have the possibility to intervene directly into the meeting, without having to request. This feature is not activated at the time the user registers on the server. It is useful for the user (i.e. for administrative delegation, or for all other high-level users) who is allowed to say their opinions in any moment.
To auto-enable on one Full-Duplex channel, you just press the Interrupt button on the toolbar with the left mouse button (or use the horizontal menu Users à Interrupt):

In this way you can choose, through the context menu, which Full-Duplex channel be enabled on.