1. The New Vulgate
First a word of thanks for his pointing out The New Vulgate available on the Vatican’s website. It was uplifting to notice this Vulgate no longer uses the incorrect word praedestinatus, but rather uses constitutus (it's the difference between predestinated and appointed). I'm still uncertain as to when this correction actually occurred. It wouldn't surprise me if Rome actually kept this error in the text as late as 1971 (the integrity of the Biblical text hasn't typically been a pressing concern in Romanism). For over four decades following Trent, little Vulgate correcting was done, and even the current corrected Vulgate has problems. David King points out:
Another instance is a corruption of Jerome's translation of Genesis 3:15b in the Vulgate. With regard to the phrase, 'He shall bruise your head,' Jerome correctly translated the Hebrew masculine pronoun (he) with the Latin masculine pronoun ipse (he). Yet, in later versions of the Vulgate, the masculine pronoun ipse (he) was corrupted by various copyists to read ipsa (she). Commenting on this corruption Calvin wrote:
This passage affords too clear a proof of the great ignorance, dullness, and carelessness, which have prevailed among all the learned men of the Papacy. The feminine gender has crept in instead of the masculine or neuter. There has been none among them who would consult the Hebrew or Greek codices, or who would even compare the Latin copies with each other. Therefore, by a common error, this most corrupt reading has been received. Then, a profane exposition of it has been invented, by applying to the mother of Christ what is said concerning her seed.
Today, the officially approved edition of the Vulgate by Rome, the Nova Vulgata Bibliorum Sacororum Editio, translates the Hebrew masculine pronoun (he) with the Latin neuter pronoun ipsum (it), which seems to be a compromise between the masculine pronoun ipse and the feminine ipsa. But the text remains incorrect compared to the accuracy of Jerome's original translation. Moreover, the corruption appears in the Roman Catholic English translation of the Douay-Rheims Bible, which reads, 'she shall crush thy head, and thou shalt lie in wait for her heel' (Gen 3:15b). This demonstrates how one corrupted translation (the Vulgate) is perpetuated in another translation (Douay-Rheims) when there is a refusal to be corrected by recourse to proper textual evidence. Although modern day Roman Catholic scholars have identified this corruption in the Latin Vulgate, it has been ignored by Mariologists who seize upon it as proof of Mary's cooperation with her seed in the crushing of the head of the serpent. [Holy Scripture, The Ground and Pillar of Our Faith Vol. 1 (Battle Ground: Christian Resources, 2001), p. 159]
2. Whose Interpretation is the Correct Romanist Interpretation?
Ignored was my question as to why the private interpretation of Augustine on Romans 1:4 becomes that which correctly interprets the Biblical text (leaving aside the obvious conundrum Augustine based his interpretation on a mistranslated text). Origen, for instance, offers quite a different interpretation. It appears (at least with this CTC commenter) to be left up to the individual as how this mistranslated verse is to be interpreted. One would think a Romanist would want to go deeper into history and rely on the older interpretation of Origen. The hosting blog CTC has no problem relying on Origen when it needs to. They quote Origen approvingly here and here. The gentleman commenting on the CTC blog chose that interpretation which harmonized with Romanism, but on what basis? It is indeed within the realm of possibility that another CTC commenter could just as easily refer to Origen and conclude: the Vulgate, with its scribal errors, did say things which contradicted the faith of Romanism.
3. The Integrity of John Calvin
John Calvin certainly wasn't immaculately conceived, nor did he live a sinless life. On the other hand, it would be wrong to attribute a wilful sin without sufficient proof. The CTC commenter says, "Calvin tried to pretend that praedestinatus was opposed to the faith and would becloud the world in darkness." He says Calvin was aware of Augustine's view on Romans 1:4, and that Calvin didn't mention it is "concerning enough." It is indeed true, Calvin cites from De praedestinatione sanctorum throughout his career. I would agree with the CTC commenter that Augustine certainly was not at a loss to offer an explanation for the mistranslated praedestinatus in Romans 1:4, and Augustine was probably not familiar with the Greek.
One thing for certain about Calvin is his high regard for Augustine and his familiarity with De praedestinatione sanctorum. It indeed is curious as to why Calvin left out Augustine's comment on Romans 1:4 at this spot in his Antidote to Trent. Anthony N.S. Lane has pointed out Calvin didn't always have access to good libraries, and also had time constraints which governed his writing ability. These could indeed be factors as to why Augustine's opinion was left out by Calvin.
Was Calvin though "pretending"? Before attributing such unscrupulous polemics to Calvin's Antidote to Trent, perhaps we should consider whether Calvin may have rather had contemporary Vulgate exegetes in mind when he stated "Those not acquainted with Greek are at a loss to explain this term." On the other hand, I would assume some of those contemporaries of Calvin offering an exegesis of the Vulgate on Romans 1:4 would have been acquainted with Augustine on this and simply followed him (or Aquinas). It would appear to me though, Calvin probably is referring to contemporary exegetes. One need only consider his repeated disdain for Vulgate supporters throughout his treatise.