Wrong required message with `opam switch create`

[Halbaroth]

In this PR: https://github.com/geneweb/geneweb/pull/2167 I have two opam files geneweb.opam and geneweb-rpc.opam. The zarith package is an optional dependency of geneweb and a transitive dependency of geneweb-rpc. If I run

opam switch create . --deps-only 

opam outputs:

  ∗ zarith                1.14     [required by geneweb]

instead of

  ∗ zarith                1.14     [required by geneweb-rpc]

I am sure that zarith is not a transitive dependency of geneweb as the following commands

opam switch create . --empty 
opam install ./geneweb.opam --deps-only 

does not install zarith and it is not present in the output of opam tree ./geneweb.opam.