So I'm not sure if this is a bug or just a soon-to-be embarrassing failure on my part, but I'm entirely unable to bring up the "invite steam friends" prompt.

I've attempted to bring it up by entering Tier 1 (Depth 0) at all four current gates, both from the mission menu and the arcade, both "form a team" and "play solo," and with the prompt option in the prompt menu both checked and unchecked.
Is there some hidden menu option in Steam or Spiral Knights options I'm missing that may be screwing with this?