WGT have given us back the ability to add a message when declining a game invitation. I for one am glad of that. But it has also brought back with it the bug that existed previously, i.e. the declining player remains red to all players except the person who invited.
Here is the workaround...
If a player declines a game invite with a message of any sort, reinvite that same player and then immediately cancel his invitation. The spot will now be free for a new player and all players in the lobby will be able to see all players that have accepted. If it was a random, make sure you know the name before clearing the declined invitation.
Once you get used to the procedure I think you'll find it's not too much hardship.
From my programming experience (although not knowing the language WGT is written in), I would say the problem is with a variable or flag not being cleared and really shouldn't be too difficult to find and fix.
Icon - would it be possible to pin this so that others can see it easily and it doesn't get lost in the depths of the forum, at least until the problem is sorted.