String contains `<My Test>` cannot be added to the post.

Expected behavior

String contains <My Test> can be added to the post.

Actual behavior

String contains <My Test> cannot be added to the post. Basically, the string containing <> will be treated as invalid HTML tags and cannot be correctly inserted to the post.

How to reproduce

Open an existing post, Put <My Test> and when you click Update Post, you will see error Please remove the following HTML elements from your post: <my>

• Browser: Chrome 63
• Operating system: Win 10 64 -bit