Abnormalities in "widget" tags

Is it possible to write code in the body with “code editor”? If you use “widget” and enter the following code, it is normal before saving the project, but after saving, characters that do not understand the meaning are added I’m sorry, does anyone know why this is?..

“Before saving”

“After saving”

<iframe-t src=“https://www.googletagmanager.com/ns.html?id=G***-********
height=“0” width=“0” style=“display:none;visibility:hidden”></iframe-t>

normal=「iframe src」
anomaly=「<iframe src」