I had “The Cloning of Shredder” and chose “Leonardo, Sewer Samurai”, in the next turn when I got my second copy, I attacked with “Featherbrained Filcher” and after blocks, I tried to Sneak cast “Leonardo, Big Brother” from my Graveyard, using “Leonardo, Sewer Samurai”'s ability. The game asked me which of the two “Leonardo, Sewer Samurai”s I would like to use and I chose one by clicking on it and “Submit”.

Then the casted “Leonardo, Big Brother” just hung in the spells area on the right with a blue “interactable” border - this is the point I would call this a bug.

I expected him to enter attacking and bring “Featherbrained Filcher” back to my hand, but instead nothing happened. I repeated this whole process once (because he was interactible, with a blue border, as I wrote). Then I tried this a third time, but this time I clicked on the other “Leonardo, Sewer Samurai” to choose the “allowed to cast from grave” effect. and this time it worked as expected.

My guess is: The second “Leonardo, Sewer Samurai” overwrote the game's first “Leonardo, Sewer Samurai”'s ability and kinda broke it, so I couldn't choose the first one and had to choose the second one.