Closing a chat topic also disables chat replies

I thought that I might want to create a topic for a chat but not have any discussion under it, only chat. If I close the topic, the chat appears, and lets me type as though I can post (and other users see “jay is typing”, I’m pretty sure), but I can’t post the chat.

There is a separate place to close the chat. I’m not sure if it’s intended that a closed topic doesn’t allow chat or if it’s a bug. If it’s not a bug, then maybe closing the topic should also close the chat?