We could resolve the issue for that particular game ourselves, but since the bug remains here is what we did:
I left the game and rejoined. No Effect.
The second player, the one were the bug had occurred, left the game and rejoined. Then the display went to 5/3:3 as it ought to be.
To clarify all what the second player had done:
- Clicked Join
- Entered the password, but with an uppercase first letter instead of the required lower case
- Nevertheless he was allowed into the lobby
- He selected a slot and color
- Then he received an error message about the mismatching password and was expelled from the lobby
- He clicked join again
- Entered the password correctly now
- When the lobby screen had loaded, he was already joined with the color that he had previously selected.
- Display then showed "6/3:3", but only 2 humans and 3 AI were joined at this time.
- He left the game and joined again, this time entering the right password. He then arrived normally in the lobby and selected color and slot, the display then showed "5/3:3" as it should.
Hope that helps to squash that nasty bug!