Bags at the non-U.S. origin always get tagged to the final destination. However, U.S. regulations require all passengers at the U.S. point-of-entry to retrieve their checked baggage after passing through immigration before being able to proceed into the main terminal area of that airport, and after passing through customs. And there are luggage "re-check" counters just prior to the exit into the non-sterile area. I'm actually quite surprised that on your previous transit connection at MIA you did not have to do this; and that your bages were automatically transfered from your inbound intl flight to your outbound one to EZE. Was your departure city from Europe DUB by any chance?