Nope, my mistake. It's actually the jump at 4:28. And the real problem was I never figured out the "double tap to run" rule. The documentation doesn't mention that.

it... isn't there? O_o

It's the jump at 4:30. The small platform you land on isn't there.

Actually, I have. Is this the jump you're referring to? http://www.youtube.com/watch?v=Gw-d9d63KGE#t=263s

Yes, I play the version on the repo. The levels haven't changed since my initial competition submission. Maybe I should make a "let's play" video of me playing this to level 7 or so :P.