Quote from TEN INCH TOM:
We have actually known about this bug, PsyMarth found it one a gamefaqs forum and then both of us found a few spots to use it in. Check out my run . I have improved the time since then but you can see the first cube I get I actually longjump to a platform that you're not supposed to be able to reach and get a "secret" cube. There are other spots to do it in that are mostly small time savers. Most major time savers with this glitch come in 100% in the sewers.
Ah okay, well I'm glad to hear you guys know about it, I would've been somewhat worried if nobody had found this simple trick haha.