Hmm... I tried on 2 recent Guix commits:

On 1564e0fefa0ccab7a4c350a158806e59274e8ea1:

--8<---------------cut here---------------start------------->8---
./pre-inst-env guix build qtwebkit
# ...
building /gnu/store/bfxanwzxmkbkd0dhcfbs0pcqq9wbbd8j-qtwebkit-5.212.0-alpha2.drv...
--8<---------------cut here---------------end--------------->8---

On abe6e670d356b8333b41c7359c0ab25a58fe736b:

--8<---------------cut here---------------start------------->8---
./pre-inst-env guix build qtwebkit
building /gnu/store/6imcxcixnsgzvh7riibx8almp5diyal0-qtwebkit-5.212.0-alpha2.drv...
--8<---------------cut here---------------end--------------->8---

Is something wrong?

-- 
Pierre Neidhardt
https://ambrevar.xyz/