Steps to reproduce the issue

Go "Administrator area" -> plugins -> TinyMCE plugin, and insert any tag (or any text) in field "Valid elements".
Go to editor in any component's settings, where exist Tiny MCE editor.
Edit text in editor and save (or click Initial code button).

Expected result

Normal formatting code.

Actual result

Formatting in editor is crash.

System information (as much as possible)

Joomla 3.7.5.

Additional comments

If field "Valid elements" in plugin's settings is empty, plugin works normal.