I'm Roman Catholic and I think they ought to fire the guy who first called them "bulls"! :P
According to the teaching of the First Vatican Council and Catholic tradition, the conditions required for ex cathedra teaching are as follows:
1. "the Roman Pontiff" 2. "speaks ex cathedra" ("that is, when in the discharge of his office as shepherd and teacher of all Christians, and by virtue of his supreme apostolic authority….") 3. "he defines" 4. "that a doctrine concerning faith or morals" 5. "must be held by the whole Church" (Pastor Aeternus, chap. 4)
There have been two pronouncements considered ex cathadra,and a lot more papal bulls;that better. The core beliefs mostly stem from the Nicean Creed and The Assumption of Mary and Immaculate conception,which came from papal bulls
I did not see an actual instance of a papal bull being overturned, but I found there is effort among Native Americans for 20+ years now for a bull of 1493 to be overturned...
"On May 4, 1493 Pope Alexander VI issued the Inter Caetera papal bull which called for non-Christian nations to be reduced and subjugated."
Apparently, so far the Vatican has said this bull is "non-juridical," but the pope has not taken the step to revoke it.
A Papal Bulls is about as Official as the pope can get. It is "from the lectern", and for the pope to change his mind about it later is just unthinkable.