ride_4ever

When you post a work to an anonymous, unrevealed AO3 collection your work is supposed to stay hidden until the collection is set to be revealed... and that is what happens unless that collection has been hit by the AO3 "reveals bug" that causes submitted fanworks to appear immediately as if you'd posted them outside the collection. The mods cannot predict or prevent the “reveals bug”. To prevent your work from being revealed ahead of time, you need to preview your work and save it as a draft, check its settings, and then either continue to post it (if the settings are correct) or delete it, wait a few minutes, and try again. And don't leave it as a draft - that will not fulfill your assignment.

Here’s a “Reveals Bug” Tutorial, courtesy of the Once Upon a Fic comm.

(TYK to feroxargentea for providing this information.)