I know that I can’t upload quodlibet since it’s already in extra, here I only use quodlibet in $pkgbase. I thought this was an appropriate use of the $pkgbase var (according to https://wiki.archlinux.org/index.php/PKGBUILD#pkgbase).
the pkgbase variable is used to group a set of **source packages** under a single PKGBUILD. Btw an AUR package (here I refer to pkgname and pkgbase as well) name must never clash with another package included in the official repositories.
There's no point to use a pkgbase for a single package, which in turn is named in a different way. Just remove the pkgbase='quodlibet' to your PKGBUILD.
For instance, I use this for krita too (https://aur.archlinux.org/packages/krita/), where the pkg differs from calligra-krita because it doesn’t depends on calligra-libs and calligra-filters (thus avoiding pulling in kdepim), since only the relevant ones for Krita are built(-in).
The same applies to krita package. Why do you use the caligra pkgbase if you only build the krita package? Your PKGBUILD doesn't build a couple of packages but only krita. Then simply remove the pkgbase='caligra' and use only pkgname='krita' instead.