Here's an interesting article from Catholic apologist Jimmy Akin: Identifying Infallible Statements. For those of you engaging Roman Catholic apologetics, this is a good read to see what sort of logical hoops one must jump through when tackling this subject.
Akin goes through the papal bull Exsurge Domine, the bull condemning Luther's teachings. Akin seemingly works hard to interpret the document to not mean anything specific. Akin argues:
1) Luther was not condemned for violating infallibly defined dogmas.
2) Luther was condemned by a whole series of propositions in globo. These propositions were  heretical or  scandalous or  false or  offensive to pious ears or  seductive of simple minds and  in opposition to Catholic truth. The Pope doesn't say which proposition holds which characteristic. The Latin of Exsurge Domine makes it clear one cannot determine the kind of censure being applied to the individual propositions.
3)One cannot even infer that the pontiff’s mind was that all of the propositions were false. The censures "heretical" and "false" both imply falsity, but "scandalous," "offensive to pious ears," and "seductive of simple minds" do not.
4) One can only speculate which censure should be applied to each proposition.
If I recall correctly, Exsurge Domine said that the Pope could, "without any further citation or delay, proceed against [Luther] to his condemnation and damnation..." The bull condemns 41 errors in Luther's writings, calling him to recant withing 60 days or be excommunicated, and decrees his writings should be burned. If ever I had to pick a lawyer to represent Luther, I would've picked Jimmy Akin.
The Magisterium: Luther, we condemned you via the reasons put forth in Exsurge Domine.
Akin: Objection! Exsurge Domine was not an infallible bull, nor did Luther violate any infallible dogma.
The Magisterium: Luther, your writings are heretical or scandalous or false or offensive to pious ears or seductive of simple minds and in opposition to Catholic truth.
Akin: Objection! Exsurge Domine doesn't say which is which, so it can't be applied to my client, and the document doesn't even infer all Luther's writings condemned are false. In fact you haven't specified anything, but have only put forth non-infallible vague statements about my client's guilt. If this doesn't make sense to you, you can call a staff apologist at Catholic Answers for further information.
Roman Catholic writer John Todd states,
"The bull [Essurge Domine] was contradictory,lacking in clarity, and incidentally far less effective than it might have been. It relied solely on Luther's writings prior to the Leipzig disputation. Thus the bull had in it the notorious statement that it is heretical to say that 'to burn heretics is contrary to the will of the Holy Spirit' and the anomalous statement that it is heretical to say that 'secular and spiritual princes would do well if they would put an end to mendicancy'."
"Eck came into the committee [preparing Exurge Domine] half way through, much o Cajetan's disgust., and was largely responsible for bulldozing a decision and the miserably incompetent text through the committee. Subsequently Eck himself said the bull was hopelessly inadequate and pointed out that in fact the committee knew very little about Luther's 'errors'. No attempt was made to refute Luther by reference either to the Bible or to the Fathers, a remarkable and unusual omission. "
Source: John M. Todd, Luther (New York: Paulist Press), 1964 p.166