Players with partial name matches to member names of another clan are getting clan login/logout messages for that clan. The cause is this line in Clan.Broadcast:

IPlayer target = Instance.players.FindPlayer(member.Value);

Looking at the way clan members are stored, I believe that this line should be:

IPlayer target = Instance.players.FindPlayer(member.Key);

This should restrict the allowed recipients of the broadcast to only the IDs of actual clan members.