My opponent quit at 00 so I hit ok and it brought me to the main menu like it normally does. While at the main menu, it said my oppent had quit again so I hit ok again. I decided to look at my replays to see if anything had changed, and it shows me winning 4 times from just one battle.

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I think that happened to me once, not a common thing but may happen...
Multiple quit signals maybe?
I also remember a weird reward screen. First a screen with double rewards, than another one with a negative reward... like the first was 11,000 credits than the second was -5,500 credits... it was likewise for the exp...
I had forgotten about it until you created this thread

Two or three times I have seen a negative rewards screen. But never as a second rewards screen. I cant say if I actually gained or lost credits tho, as I didnt know the amount of credits before hand - I assumed it was just a mistake by the computer to display a negative...

Edit to add
Here is a screen shot of a negative reward screen that I got today.
I think that I actually was awarded a positive gain in credits, but I am not 100% sure.