title: selenium python driver, function: move_to_element_with_offset incorrect behavior
body: <p>I face a problem with selenium python driver, function: move_to_element_with_offset
  It seems that the function only move mouse to the middle of the element</p>
  
  <pre><code>def setUp(self):
  
      print "hello"
      self.logger = setuplogging()
      self.browser = webdriver.Firefox()
  
  def _test_add_point(self):
  
      body = self.browser.find_element_by_tag_name("body")
  
      body.send_keys(Keys.UP * 20)
      applet = self.browser.find_element_by_id("selected-applet")
      pics = applet.find_elements_by_xpath(".//div[contains(@class, 'picture')]")
  
      time.sleep(5)
      real_pic = pics[0].find_elements_by_xpath(".//img")
      action_chains = ActionChains(self.browser)
  
  
      action_chains.move_to_element_with_offset(real_pic[0], 20, 20).perform()
      time.sleep(5)
      action_chains.click().perform()
      time.sleep(10)
  </code></pre>
  
  <p>When i execute the code above, it will always click to the middle of the picture, when my expectation is that it will click to the center plus offset (20, 20) in this case. Changing the offset won't help. Using the function move_by_offset won't help also.</p>
  
  <p>Could you please help?</p>