WYSIWIG editor description field styles

Your software
My Mautic version is: 2.16.0
My PHP version is: 7.1.33-12+ubuntu18.04.1+deb.sury.org+1

Your problem
My problem is: WYSIWYG puts default attribute styles even when the values are manually removed.

Here are the default styles:

Then the style attributes are deleted manually,

but then they appear again…

They also appear on the website where the form is inserted.