inherit_mode is ignored for arrays other than Include/Exclude if also inheriting non-default configuration (with inherit_mode at cop level)

[Drowze]

Expected behavior

I expect to be able to merge my configuration with rubocop default configuration, even if I also inherit a non-default configuration.

Actual behavior

At the project .rubocop.yml, if I define an array that already exists within rubocop's default configuration, my configuration overwrites' the default config, even if inherit_mode is set to merge on the cop level

Steps to reproduce the problem

Given a hosted configuration (gist here):

AllCops:
  NewCops: enable

Naming/VariableNumber:
  EnforcedStyle: snake_case
  Exclude:
    - foo.rb
  Include:
    - bar.rb

And given .rubocop.yml:

inherit_from:
  - https://gist.githubusercontent.com/Drowze/0ea51fa5bf3cbec9e280f2f913be57df/raw/eaa3ac4911b982ddf933e32e4f53d91c41cebb43/rubocop-test.yml

Naming/VariableNumber:
  inherit_mode:
    merge:
      - AllowedIdentifiers
      - Exclude
      - Include
  AllowedIdentifiers:
    - iso2
  Exclude:
    - test.rb
  Include:
    - another_test.rb

When I run rubocop --debug --show-cops Naming/VariableNumber I get this output:
(note that AllowedIdentifiers does not include capture3 or any of the items defined at the default configuration)

For /Users/Drowze/r/rubocop_bug9: configuration from /Users/Drowze/r/rubocop_bug9/.rubocop.yml
configuration from /Users/Drowze/r/rubocop_bug9/.rubocop-https---gist-githubusercontent-com-Drowze-0ea51fa5bf3cbec9e280f2f913be57df-raw-eaa3ac4911b982ddf933e32e4f53d91c41cebb43-rubocop-test-yml
Default configuration from /Users/Drowze/.asdf/installs/ruby/2.7.3/lib/ruby/gems/2.7.0/gems/rubocop-1.19.0/config/default.yml
Naming/VariableNumber:
  Description: Use the configured style when numbering symbols, methods and variables.
  StyleGuide: "#snake-case-symbols-methods-vars-with-numbers"
  Enabled: true
  VersionAdded: '0.50'
  VersionChanged: '1.4'
  EnforcedStyle: snake_case
  SupportedStyles:
  - snake_case
  - normalcase
  - non_integer
  CheckMethodNames: true
  CheckSymbols: true
  AllowedIdentifiers:
  - iso2
  Exclude:
  - "/Users/Drowze/r/rubocop_bug9/foo.rb"
  - "/Users/Drowze/r/rubocop_bug9/test.rb"
  Include:
  - bar.rb
  - another_test.rb

Finished in 0.111557999975048 seconds

From my test I also found:

• if I move inherit_mode to the root level, AllowedIdentifiers is merged correctly
• if I do not inherit configuration (via inherit_from or inherit_gem), AllowedIdentifiers is merged correctly

RuboCop version

$ rubocop -V
1.19.0 (using Parser 3.0.2.0, rubocop-ast 1.10.0, running on ruby 2.7.3 x86_64-darwin20)