Strange Argentinian variety

I have several  of these bills, and when I looked closely at them, I noticed something strange about the positioning of the serial number on one of them.

 The bill on the bottom has the regular red serial number on the side, but the top one is black and on the bottom.

 Is this some strange variety, or an error, or what?

The black horizontal serial number is this variety: 

This difference is likely due to the fact that, unlike all other variants, this one was printed at Casa da Moeda do Brasil instead of Casa de Moneda, Buenos Aires.