This has happened to me before and happened again today on game #40234876 oregon
i will have my first turn be 5 coppers. yay!
then my second turn will be.....5 copppers. yay! but should be impossible, no?
From the log of that game, it looks like you had a 2/5 opening, so you did nothing on turn 1 and drew the 5 Copper for turn 2. On turn 2 you played 5 Coppers to buy Mountebank, then discarded everything, shuffled your deck and by shuffle luck drew again 5 Coppers for turn 3.
So don't forget turn 1, even you didn't do anything in it.
An excellent lesson on why it's critically important to write down game numbers. What sounded like a huge game bug was able to be investigated, and the player's oversight was able to be identified immediately. Nicely done all around! :-)