When I try to create a game, I see the players' names who are trying to join but it's like they aren't pressing the 'ready' key because I don't see them fully so a game can start.
And I'd be willing to bet what they see is their name above the scrolling avatars in the lobby with the "joining" circle spinning.
I found out that happens if you accept an invite while you're playing a single round. If you accept the invite it prompts you you'll lose the current game. When you say OK you get to that picture above.
The only thing I haven't tried yet is closing the game before accepting the invite. I suspect that'll fix it for now.