Tell Everyone Why We Do It This Way
All groups have norms--expectations about how the group does things. For formalized teams or Boards or Committees, once the group has been in existence for a while, the group norms become unspoken. Everyone knows them or can observe them fairly easily and learn to play by the rules.
Until you get someone who doesn't. And then it can be a big problem, because when you try to negotiate with that person, you often start from a position of "Why is this person violating the rules so egregiously?" The problem is, they never understood the rules like you do. We each see the world differently and bring different backgrounds to the same situations, so we will interpret them differently.
Which is why you need to talk about the rules and expectations, particularly as new people enter the group. And to be honest, even after you say what the culture of your group is out loud, people will still end up understanding it differently. But when they do, you at least have something to point back to when you confront that person on violating the norms. It will serve as an opportunity to have a clarifying conversation about expectations and what really works in this group, as opposed to a personal conflict where one person is being blamed for doing things wrong.