Iframe do not work om upfront

When I put in this iframe code in the post, it do not display.
<iframe src="http://www.finn.no/pw/search/car-norway?orgId=1273503730"
width="100%" height="700" frameborder="0" scrolling="auto" />

https://www.listerbobil.no/wp-admin/post.php?post=597&action=edit

But when I use the same code on an non WPMUDEV theme it works...