I think it depends upon whether the meaning of "infallible" is restricted to men definitively proclaiming a doctrine of faith or morals, or being a source incapable of deceiving or being in error. And of course, RCs (as well as Prots) debate the precise meaning of inerrancy.
The issue of whether Scripture is infallible has been inconclusively debated much on Catholic forums, as I know of no "official" (that also being an issue of some debate) teachings that explicitly states that Scripture is infallible or is not infallible, though i think papal affirmations of it weigh stronger in the direction of infallibility.
I think the assertions by RCs that Scripture is not infallible are often driven by the desire to elevate the authority of the Roman magisterium above Scripture, which in fact, it effectively presumes even though it comes short of claiming Divine inspiration.
As the Catholic Encyclopedia states,
Inspiration signifies a special positive Divine influence and assistance by reason of which the human agent is not merely preserved from liability to error but is so guided and controlled that what he says or writes is truly the word of God, that God Himself is the principal author of the inspired utterance;
but infallibility merely implies exemption from liability to error. God is not the author of a merely infallible, as He is of an inspired, utterance; the former remains a merely human document. http://www.newadvent.org/cathen/07790a.htm
However, this definition does not leave Scripture to be less than infallible unless one holds that it is liable to teach error, while it claims infallibility for a human document lacking Divine inspiration (but not protection) in contrast to Peter's confession and the rest of Scripture.
A Catholic poster who argues on "Catholic answers" forum (http://forums.catholic.com/showpost.php?p=3614383&postcount=1) for Scripture being infallible sees denying infallibility to Scripture as being based on faulty logic and "uncharitable, especially given the number of times that This Rock has used the word infallible in exactly the same way." as,
This Rock has used infallible to describe decrees, statements, definitions, dogmas, documents, doctrines, professions of faith, teachings, catechisms, canonization, Sacred Tradition, the Apostles Creed, the Nicene Creed, the Athanasian Creed, and even the Summa Theologiae of St. Thomas Aquinas.
I think the reason some RCs teach that Scripture is infallible is because they see it as impossible for it not to be so if God is the author of it, (CCC 105) and "the books of Scripture firmly, faithfully, and without error teach that truth which God, for the sake of our salvation, wished to see confided to the Sacred Scriptures," (CCC 107) and is otherwise stated by their church to be inerrant.
And as said, the premise of some that it cannot be infallible because it can be misunderstood is also true of the Magisterium, which has infallibly declared that it is (conditionally) infallible.
These teachings of the Ordinary Magisterium are referred to by then Cardinal Ratzinger, with particular wording, as the non-infallible teaching of the Magisterium and non-irreformable magisterial teaching, in the document issued by the Congregation for the Doctrine of the Faith called 'The Ecclesial Vocation of the Theologian,' n. 28 and 33. This wording demonstrates Cardinal Ratzinger's understanding that not all Magisterial teachings are infallible or irreformable.
In the same Address to the U.S. Bishops cited above, Pope John Paul II said: With respect to the non-infallible expressions of the authentic magisterium of the Church, these should be received with religious submission of mind and will. Clearly, the term religious submission of will and intellect refers to the ordinary non-infallible teachings of the Magisterium and is a different degree and type of assent than the divine and Catholic faith due to infallible teachings.
Therefore, the Magisterium can teach both infallibly and non-infallibly. Heresy is the denial or obstinate doubt of the infallible teachings and also of those ordinary teachings which are essential to salvation; heresy is a refusal to give the full assent of faith due to those teachings. The denial or doubt of non-infallible teachings in general might also be sinful and culpable, but the sin is not generally the sin of heresy and is a lesser matter, because the assent required is a lesser degree of assent.
The teachings of the Ordinary Universal Magisterium (i.e. the Universal Magisterium) are certainly infallible, but these are distinguished from the non-infallible, non-irreformable teachings of the Ordinary Magisterium themselves, whose number and extent cannot be trivial. Those who claim that nearly every teaching of the Ordinary Magisterium actually falls under the Universal Magisterium are in effect extending infallibility to the Ordinary Magisterium itself, because the teachings they claim to be infallible under the Universal Magisterium have not in fact been taught universally by the Church. Such persons also err grievously by reducing the kind and number of the teachings of the Ordinary Magisterium, so that no ordinary teachings are left of any significance.
This article from the link concludes with:
So, I wonder how many "faithful" Catholics can even know what teachings they are being given are, by their own estimation, fallible or infallible? I know when I was Catholic there was no room for doubts of anything I was taught and to question was deemed a sin. Why the need for such legalese for something, admittedly, was only actually used once???