Rails weird behaviour with rails destroy migration

Working on rails, i have noticed following behaviour with rails migration. I Don't know is it expected behaviour or not. Is anyone have any idea about it?

Step 1 - I have created a migration

rails g migration CreateCustomer

Result of this command -

  invoke  active_record
  create  db/migrate/20151012160803_create_customer.rb

Step 2 - Now i want to Undo code generated with above command.

rails d migration CreateCustomer

Result of this command -

  invoke  active_record
  remove  db/migrate/20151012160803_create_customer.rb

Step 3 - if i run the step 2 command rails d migration CreateCustomer again, i get differant results on different rails versions

Result on Rails 3.2.17 is -

  invoke  active_record
  remove  migration.rb

Result on Rails 4.0.0 is -

  invoke  active_record
  remove  create_table_migration.rb

My question is why rails removing migration.rb or create_table_migration.rb file? is rails really removing this files?

Thanks!