Why does the phrase '[video online]' get removed when I publish a post?

I'm doing a thing on wordpress where I have to cite some sources, and I'm using a Harvard style. This includes citations for web video, and in cite lists and bibliography you indicate this through the phrase '[video online]'. However, I have noticed that whenever I do this and hit publish, that specifically gets removed.

This doesn't apply to any sources that are just noted as '[online]' - pretty much any text-based online page, there seems to be something about the phrase '[video online]' that WP just decides to delete. Does it conflict with some kind of embed code or something?