title: Watir's ability to find element in iframe depends on previous code
body: <pre><code>@browser = Watir::Browser.new #:phantomjs (same with firefox)
  @browser.window.maximize 
  
  @browser.goto 'http://www.romnation.net/'
  
  size = ['728', '90']
  p @browser.iframes(width: size[0], height: size[1]).length
  @browser.iframes(width: size[0], height: size[1]).each do |ifr|
      p ifr.img.src if ifr.img.present? # 1
  end
  
  size = ['160', '600']
  p @browser.iframes(width: size[0], height: size[1]).length
  @browser.iframes(width: size[0], height: size[1]).each do |ifr|
      p ifr.img.src if ifr.img.present?
  end
  </code></pre>
  
  <p>This program will say that there are no iframes (160, 600) on a page (even though there are). If I don't search for (728, 90) iframes first, program always finds (160, 600) iframes. Further more, it happens only if I don't only search for (728, 90) iframes first, but if I search for images (line 1) in these iframes also.</p>
  
  <p>Why on earth may that be? Am I missing something?</p>