When you start Dota2 all your chat rooms show just 1 person (you), if someone writes into it count increases, the number of people with the name list is fixed after you click the round arrow refresh button, but it's still showing current number of people at the moment of refreshing, so if you want to see actual number of people you need to click it again (it happens sometimes that it shows more then max limit of 1000 people (when after refresh there is 1000 and someone new is writing then it adds him to the count, even the left persons are already out)).
This needs to be fixed so chat rooms manage to show actual count of people themselves (like in Fb chat or Twitch chat)