[v4] clearing namespace for corePlugin doesn't work

[rj-elias]

What version of Tailwind CSS are you using?

v4.0.0-alpha.30

Reproduction URL

https://play.tailwindcss.com/bjEOmfVaL9

Describe your issue

@theme {
  --background-color-*: initial; /* DO NOT WORK: doesn't clear the background color namespace */
  --background-color-brand: blue; /* WORKS: extends the background color namespace with brand */
}

--background-color-brand: blue; works. It extends the background color namespace with 'brand'

--color-*: initial; works. It clear the whole color namespace
--background-color-*: initial; doesn't clear the background color namespace