bug: nixpkgs.config.allowUnfreePackages not combining between functions

[lazulyra]

Are you following the right branch?

• My Nixpkgs and Home Manager versions are in sync

Is there an existing issue for this?

• I have searched the existing issues

Issue description

When using nixpkgs.config.allowUnfreePackages within HM, values do not combine between functions (as is intended)

{
  config,
  inputs,
  lib,
  recursiveImport,
  ...
}: {
  home-manager = {
    extraSpecialArgs = {inherit inputs;};
    users = {
      lyra = lib.mkIf config.users.users.lyra.enable {
        imports =
          [
            ({...}: {nixpkgs.config.allowUnfreePackages = ["456"];})
            ({...}: {nixpkgs.config.allowUnfreePackages = ["123"];})
          ]
          ++ (recursiveImport ./lyra); # this does contain further allowUnfreePackage definitions, but these have no effect on the result
      };
    };
  };
}

results in

nix-repl> nixosConfigurations.thegosis.config.home-manager.users.lyra.nixpkgs.config.allowUnfreePackages
[ "456" ]

When used outside of home manager (in my case, NixOS configuration)
(shortened for brevity)

nixpkgs.lib.nixosSystem {
  specialArgs = {
    inherit inputs host recursiveImport;
  };
  modules =
    [./home home-manager.nixosModules.default]
    ++ [({...}: {nixpkgs.config.allowUnfreePackages = ["123"];}) ({...}: {nixpkgs.config.allowUnfreePackages = ["456"];})];
};

results in

nix-repl> nixosConfigurations.thegosis.config.nixpkgs.config.allowUnfreePackages
[
  "456"
  "123"
]

Maintainer CC

No response

System information

$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.18.12, NixOS, 26.05 (Yarara), 26.05.20260217.0182a36`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.31.3`
 - nixpkgs: `/nix/store/dx2qikyb4dyb6hbdfywbmsyla0z5a1h3-source`