Found another glitch: Under the ACP > Edit User, when you manually add a user to a group that's also a joinable one. Checking the group under "Secondary User Groups" will not automatically set it under "Joinable User Groups," however if you check the group under "Joinable User Groups" it will set it under "Secondary User Groups" upon submitting the edits.
Related to this, I also noticed that if you manually add under "Secondary User Groups" and they're in the Moderation Queue they'll remain in the queue as a result. I'm guessing this would mean someone could request to join the group if they're already a member of the group; if set manually under "Secondary User Groups."
I'm not sure how this impacts accessibility to the group, or if it matters, but it would be nice if checking it either way was consistent and clear the member from the queue if done manually via the ACP; either way.
Thanks.