CKEditor loading from Mail Sending impacts the Save action

1. Login with Admin and go to http://localhost:8080/xwiki/bin/admin/XWiki/XWikiPreferences?editor=globaladmin&section=emailSend
2. Configure the Mail server and click on Save button.

Actual result:

• After you click on Save button, browser displays a pop-up, asking you:

  Do you want to leave this site?
  Changes you made may not be saved.
  Leave / Stay
  

• After you click on Leave option, the page is reloaded and the configuration is saved.

Expected result:

• This pop-up will be for sure confusing for the user. He can think that his configuration wasn`t saved after clicking on Save button.
• I expect to not see anymore this browser pop-up.