Sorry for the long delay... :(

>   I think it can happen only if you added it to
> GUIX_PACKAGE_PATH, did you?

No I did not:

--8<---------------cut here---------------start------------->8---
(getenv "GUIX_PACKAGE_PATH")
$5 = "/home/ambrevar/.guix-packages"
--8<---------------cut here---------------end--------------->8---

So the issue is something else.  Any idea?