Ruby inconsistency in constant lookup

lookupfailure.rb

module A
  module B
  end
end

module C
  include A

  puts B.inspect # => A::B

  class D
    puts B.inspect rescue puts 'failed' # => failed
  end

  # Setting B inside C allows it to be found as expected.
  B = B

  class E
    puts B.inspect # => A::B
  end
end