I've had similar issues on my iPad but found that the problem was iOS caching.
Steps I took to troubleshoot:
- download using Safari on iPad (got old version)
- download using Chrome on iPad (got old version)
- restart iPad and redownload (got old version)
- download using a new install of FirefoxPortable on PC (got new version)
- download using my smartphone (got new version)
Alas, short of a nuclear option (clear all cookies and browsing history), I don't know of any fixes. I just downloaded the book from Dropbox instead.