When I paste the iframe code directly into the source code view of TinyMCE and click save it changes the code to:
View TinyMCE code after saving adds </p>
<iframe src="http://maps.google.co.uk/maps" width="425" height="350" frameborder="0" marginwidth="0" marginheight="0" scrolling="no"></p></iframe>
View HTML source of HTML page:
<iframe src="http://maps.google.co.uk/maps" width="425" height="350" frameborder="0" marginwidth="0" marginheight="0" scrolling="no"/>
Original iframecode
<iframe src="http://maps.google.co.uk/maps" width="425" height="350" frameborder="0" marginwidth="0" marginheight="0" scrolling="no"></iframe>
This is effecting the rest of the page layout and breaks the footer.
I am using Silverstripe 2.4.5 if this helps.