You shuffle 4 cards back into the deck and then you draw almost the same cards back.
Similar problems with switcheroo, reload and card trader. After so many updates you thought the development team would have patched this bug already but no this glitch is still here. At this point I am pretty sure the development team simply does not care at all or just intentionally want to screw the players. Either way it is bullshit.
it is def a bug; I run two copies in a Cerberus deck and it consistently draws the same cards I put back in my deck at a ratio if all but one. Basically, expect one of the cards used w/ Mallet to come back different and the rest the same no matter how many are shuffled back into deck