So hopefully you can see from the comments on the original question that this issue was a matter of testing, not the code.
Lessons learned here:
- If your checksums match, make damn sure your files aren't in fact, identical. That's 1000x more likely to be the case than some weird fringe case (as I originally figured it was)
- If you provide an actionable item in your Stack Overflow post (like 'download my video to see for yourself'), you should probably test that out yourself.
So I guess this question is now at least good as a) a reference for uploading files via FTP using Python and b) a good lesson on asking questions on Stack Overflow!