After finding three separate occurrences in my students' papers of the claim that Augustine changed his mind from view A to view B, I decided to try to track down where this was coming from:
View A: Death is punishment for original sin.
View B: Death is natural, so it is good.
One of them cited this entry on Augustine in the Encyclopedia of Death and Dying in his bibliography. It says the following:
Augustine's evaluation of death undergoes a profound change after he encounters the theology of Pelagius. In his earlier writings, such as On the Nature of the Good, Augustine regards death as good because it is natural: Death is the ordered succession of living entities, each coming and going the way the sound of a word comes and goes; if the sound remained forever, nothing could be said. But in Pelagius's theology, Augustine encounters a radical statement of the "naturalness" of death: Even if there had never been any sin, Pelagius says, there would still be death. Such an understanding of death is very rare in early Christianity, and Augustine eventually stands with the mass of early Christian tradition by insisting upon the exegetically derived (from the Pentateuch) judgment that death is a punishment that diminishes the original "all life" condition of human nature. It is a distinctive and consistent feature of Augustine's theology of death that it is developed and articulated almost exclusively through the opening chapters of the Book of Genesis.
Now I've never read that earlier work, so I have no idea if this is even true (and I don't have it, so I can't even check), but it's the only thing I can find that remotely deals with such a view from Augustine, and I checked several pages deeper in Google after I found this. So I'm guessing this is the source for all of them and not just the one, and the rest all failed to include it.
The problem is all five students (I went looking through the stack to see if any others did this, and I found another two) got the order backwards. They all said that Augustine originally held view A and then held view B. The website says he first held view B and then changed to view A. One of them did mention Pelagius, but the others left that out. None of them mentioned the use of actual biblical arguments for changing his mind, but then they didn't think he was changing it to the biblical view but from it, not that they probably even knew which view was biblical.
Unless all these students have the same exact problem in gleaning information about the order of these views from this same text, there must have been either another source common to all of them besides this site, or one of them was the source for the others, perhaps the one who actually cited it. I'm not finding any other site that even mentions a change in his views on this. Some of them mentioned other internet sources, so why would they leave this out? Redaction criticism is hard.
None of this fits well with the assignment anyway, since what I was looking for was Augustine's view of the afterlife as a comparison with Socrates and Epicurus' arguments for not fearing death. But, as the title of this post suggests, those are the hazards of using Google for sources instead of paying attention in class or actually looking to the primary sources that I assigned.