Nixpkgs: texlive.combine results in non-reproducible derivation

[typetetris]

Describe the bug

Using texlive.combine results in non-reproducible derivation.

To Reproduce

Content of tex.nix:

{ nixpkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/4c817f9d6e6a4e6ddb0c51dcb093a8e70adaf5c4.tar.gz") {} }:
nixpkgs.texlive.combine {
    inherit (nixpkgs.texlive) scheme-small xpatch phonenumbers helvetic supertabular booktabs xtab xecjk;
  }

The SHA was master as of today 2020/11/5 12:45.

First

nix-build tex.nix

and then

nix-build --check tex.nix

results in

...
Wrapping './bin/tlshell' Warning: unknown shebang '/usr/bin/env wish' in '/nix/store/ssqlggvl0zvv5wldmybj80dj54kgbgv2-texlive-tlshell-56461/scripts/tlshell/tlshell.tcl'
Wrapping './bin/updmap-user' and patching shebang '/bin/sh'
derivation '/nix/store/bsi2f3qjvzh3699jrhwmz7jp3scz5rb4-texlive-combined-2020.drv' may not be deterministic: output '/nix/store/fjb02b46nq25iaw1vq9139lz3a2sjw18-texlive-combined-2020' differs
error: build of '/nix/store/bsi2f3qjvzh3699jrhwmz7jp3scz5rb4-texlive-combined-2020.drv' failed

Expected behavior
Getting a reproducible derivation.

Notify maintainers
@vcunat @veprbl @lovek323 @jwiegley

[typetetris]

diff -r of the derivation with its check from nix-build -K --check tex.nix attached.
diff.nix-build.K.check.tex.nix.txt