Paperclip: strange mime type on windows

I partially solved using this plugin to get correct mime from extension:
http://code.google.com/p/mimetype-fu/

And in my model i added:

  validate :validate_content_type

  protected

  def validate_content_type
    errors.add(:file, "Format #{File.mime_type?(file.path)} is
invalid!") unless File.mime_type?(file.path) == "application/pdf"
  end

If somebody want to get better this code will be appreciated
Thanks in any case