This is regarding r40356, as installed on en.wikipedia.org.
If the page has been deleted and then undeleted since the last edit, an attempted edit using the API will fail with an error message "The page has been deleted since you fetched its timestamp". This can happen if an admin is trying to remove vandalism from the public page history: he deletes the page, and then undeletes all but the troublesome revision.
For example, [[en:Talk:Cambrian explosion]] currently shows that it was most recently edited on September 13, while the logs for that page show it was deleted and undeleted on September 16. The timestamp picked up from the rvprop query is of course 20080913031053 from the edit.
If the "touched" date from prop=info would work to prevent edit conflicts, a fix could be to just change the documentation of basetimestamp to suggest using that instead of rvprop's timestamp (unless "touched" isn't really updated by undeletion?). Otherwise, intoken would probably have to return the appropriate basetimestamp explicitly in addition to the edit token.