Contao news and tag <iframe> and "Allowed HTML tags"

Hello

I'm running a Contao 2.9.5.

In System / Settings I have added under "Allowed HTML tags" <iframe>

Then under a news. I'm going in HTML mode with the "html" button. If I add an iframe of dailymotion (as dailmotion request to do it to make the integration of a video), the iframe tag is removed

<iframe frameborder="0" width="x" height="y" src="http://www.dailymotion.com/embed/video/xwmgct"></iframe>
text par text

give me that :

text par text

why is iframe removed if I add it under "Allowed HTML tags"?

Thanks

Edit file
/system/config/tinyMCE.php

replace

Code:

---

extended_valid_elements : "q[cite|class|title]",

---

with

Code:

---

extended_valid_elements : "q[cite|class|title],iframe[src|width|height|name|align|frameborder]",

---

reload, I hope it will work.