`legacy` mode not working for `prose-{element}` modifiers

[Folyd]

What version of @tailwindcss/typography are you using?

The latest version typography installed by Tailwind standalone CLI

What version of Node.js are you using?

No Node.js. I'm using the latest Tailwind standalone CLI

What browser are you using?

Safari and Edge

What operating system are you using?

macOS 10.15.7

Reproduction repository

https://github.com/zineland/zine

Describe your issue

After I enable the legacy mode according to #255, Tawilwind still renders prose-h1:text-center with :where clauses.

<article class="prose prose-h1:text-center">
</article>

.prose-h1\:text-center :is(:where(h1):not(:where([class~=not-prose] *))) {
    text-align: center;
}