When teacher log-in-as student, every iframe in the course page disappear.

Steps:

1. Create course.
2. Add Label to any section.
3. In the label, add the html:   

   Text before <br><iframe src="https://example.com"></iframe><br>text after<br>

1. Validate the teacher can see the page.
2. go to Participants, and click on student
3. Log-in-as the student.
4. Go back to the course, and see that the iframe is not there, but the text is there.

The problem is that the student is capable to see the iframe, but when the teacher logged in as the student, it not possible.

also happens with admin logged-in-as teacher.