yardsticks and yards coverage don't match

[NobbZ]

I have the following output:

$ rake yardstick
YARD-Coverage: 65.0% (threshold: 80%)
rake aborted!
YARD-Coverage must be at least 80% but was 65.0%
/home/nobbz/.rvm/gems/ruby-2.2.0/gems/yardstick-0.9.9/lib/yardstick/rake/verify.rb:108:in `assert_meets_threshold'
/home/nobbz/.rvm/gems/ruby-2.2.0/gems/yardstick-0.9.9/lib/yardstick/rake/verify.rb:55:in `verify_measurements'
/home/nobbz/.rvm/gems/ruby-2.2.0/gems/yardstick-0.9.9/lib/yardstick/rake/verify.rb:81:in `block in define'
Tasks: TOP => yardstick
(See full trace by running task with --trace)

$ rake doc
Files:           5
Modules:         1 (    1 undocumented)
Classes:         4 (    4 undocumented)
Constants:       3 (    3 undocumented)
Methods:        10 (    1 undocumented)
 50.00% documented

The rake-tasks are defined as follows:

require "yard"
YARD::Rake::YardocTask.new(:doc) do |t|
  t.files    = ['lib/**/*.rb']
  t.files   += ['-', 'README.md',
                    'LICENSE.txt',
                    'CODE_OF_CONDUCT.md']
  t.options  = ['--markup-provider=redcarpet',
                '--markup', 'markdown']
end

require 'yardstick/rake/verify'
Yardstick::Rake::Verify.new(:yardstick) do |v|
  v.threshold = 80
end

So as you can see, yardstick finds 15% more of my code documented than yard self does.