When requesting a rematch on the end screen of a Card Battle, but the opponent declines, the “Winner” plaque will appear above the “Winner”/“Loser” plaque of the game played.
The rest of the info, such as Captured Cards and Stakes won/lost stay as before.
You can also see that the previous plaque does not disappear, as it’s particles can still be seen if you look closely.
Here are 2 videos of me demonstrating the bug with an alt account. My alt doesn’t have an advanced deck, so I couldn’t demonstrate it, but it also happens in Advanced Battles:
