This will be fixed in the next API build. (No app update required.)
The list of versions comes into the API as
1, 2, 3 and has to be reversed to get
3, 2, 1. Since the API can return revisions for multiple posts, these get shuffled together using a reverse sort. Unfortunately the reverse sort algorithm is stable and preserves the order of items with the same timestamp giving us
2, 3, 1.
The solution was to reverse the entries before applying the sort so 3 and 2 are in the correct order before sorting (and really no sorting has to be done for one post in this case).