Wordpress - TinyMCE custom styles remove class when switching styles

Seems the question was asked at community.tinymce.com and the answer is here: https://community.tinymce.com/communityQuestion?id=90661000000IiyjAAC

You can't make the style you've defined remove any previous classes, but what you can do is 'apply' the style again by selecting it from the dropdown list and it will be removed - i.e. the class will be removed from the tag. You can then choose a different style from the drop-down list and the class relevant to that style will be added to the tag.