This has happened to me too, getting a ranked loss message after switching from playing ranked to non-ranked Standard. I even switched decks after the 1st non-ranked match and it still occurred.
Edit: As noted by some others, this seems to only be visual, at least in my occurrence. I tried getting this bug again by losing a ranked match and had my rank decrease. I then went into a non-ranked match and won. After the win, I had the rank decrease display again. I have attached a log showing this occur. While this is only visual, it does cause confusion and worry about rank being affected in non-ranked games, as all of the reports given show.
This has happened to me too, getting a ranked loss message after switching from playing ranked to non-ranked Standard. I even switched decks after the 1st non-ranked match and it still occurred.
Edit: As noted by some others, this seems to only be visual, at least in my occurrence. I tried getting this bug again by losing a ranked match and had my rank decrease. I then went into a non-ranked match and won. After the win, I had the rank decrease display again. I have attached a log showing this occur. While this is only visual, it does cause confusion and worry about rank being affected in non-ranked games, as all of the reports given show.