Since nobody replied so far, I'm gonna go out on a limb and suspect that VS uses the text within the submission box to check for dupes, not the embed code it generates from it. You still can't submit it though, because a second check is done when you hit the continue button.

Workaround would be to generate the embed code, copy-paste it over itself, then hit the validation button.

redacted

sorry, nevermind. Just me being frustrated.

Comment hidden because you are ignoring dag. (show it anyway)

Does VS' submission checker not handle redirectors?

Possibly not. Lucky might have more light to shed on this.

What happens if you just hit validate a second time in this case?

"This video has already been submitted (view existing video)". It should catch that in the first time.

Because clicking the button twice is too hard?

Um, how? After "Your embed looks good!", the button is greyed out.

Hmm... OK, missed that bit.

I just tried it, and if you know you are submitting a redirect url, you could click in the box, select all, and copy, and the box ungreys. You don't even need to paste... then click validate and it works.