Hi,

In commit 
https://git.savannah.gnu.org/cgit/guix.git/commit/?h=core-updates&id=ccc2658e2a111590ec25e308946e47a24d357785, 
the default 'strip-flags' and 'strip-directories' argument were changed 
from a S-exp to %strip-flags and %strip-directories from (guix 
build-system gnu).

This is fine, except for copy-build doing (sexp->gexp ...) on those, 
even though %strip-flags etc. are G-exps, not S-exps, causing errors like

> ice-9/read.scm:126:4: In procedure read-expr*:
> /gnu/store/abb0wz0223bjsxkw9av768szz955m2xh-openjpeg-data-2021.09.26-builder:1:2504: Unknown # object: "#<"
> builder for `/gnu/store/qbc93ywsbm3bwwiqn7h8fv124i1yqh53-openjpeg-data-2021.09.26.drv' failed with exit code 1
> derivation '/gnu/store/qbc93ywsbm3bwwiqn7h8fv124i1yqh53-openjpeg-data-2021.09.26.drv' offloaded to '141.80.167.174' failed: build of `/gnu/store/qbc93ywsbm3bwwiqn7h8fv124i1yqh53-openjpeg-data-2021.09.26.drv' failed


Changing '(sexp->gexp strip-flags)' to 'strip-flags' and likewise for 
'strip-directories' should fix things (unverified).

Greetings,
Maxime.