Earlier today, when I was playing a Solo Arena match, my internet disconnected. When I re-connected and logged back on, the game had not yet registered me as receiving a loss. I re-fought and defeated the opponent I had disconnected from and beat them; the game registered a win. A few wins later, however (I forget how many) that opponent became listed as a loss and I had to re-fight them. As a result, the game thought I had beaten that opponent twice, so by the time I was about to fight the final boss it listed me as having 9 wins:
This included the extra card prizes after each victory; I ended the run with a 39-card deck (note the lower-right corner):
That said, after I finished the arena the game logged me as having the correct number of wins (I lost twice to the final boss & ended up with 8 wins). Still, I assume this is not correct behavior so I thought I'd report it.