1. I download the software, under the above license, and put it on my FTP
server.
2. The license changes; it now says "redistribution of any kind is prohibited".
3. You mirror my FTP server. (I can still send it to you, since I'm under
the original license.)
4. You make your mirror available as an FTP server.
You have the new license, since you downloaded it after the license
revision. Your redistribution of the software violates the license.
It may be very hard to notice this, though, if what you're mirroring
is the non-free archive in whole: you can't assume much about non-free,
but you should at least be able to mirror it safely.