This probably means you're either using an out-of-synch mirror or there was a problem in the network transfer.
The latter turned out to be the case. This is really funny, though. I maintain a CPAN mirror on a local machine and refresh it once a week, so I had ruled out either of those scenarios. Somehow, cpanp pulled the file and it had 0 size. I'll try to track down how that happened in the code and maybe even fix it. My suspicion is that I had a full disk at the time (dl'ing too much anime ;) Thanks for all your help!
The only easy day was yesterday