Well, folks… it looks like the Mount and Blade key saga has come to a close.
After sending in a ticket to be sure that my issue was addressed with regard to the CD Key issue, I fired up Steam an hour ago and noticed that it downloaded something for Mount and Blade Warband. As I thought, it was a fix to allow players full access to their game.
I played the game for an hour and everything seems fine now. No ads when exiting, and no demo version notice when starting up the game.
All well and good then. Just restart Steam, and you should be good to go. For more information on the game though, feel free to check out my impressions piece written a few hours ago. Cheers!