C5 freezing

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I have a site on 8.5.5 and when I go to Dashboard->System&Settings->Basics->Rich Text Editor under Editor Plugins is a long list of check boxes and a preview showing how my changes will affect the look of the editor.

If I check the box next to Add And Remove Classes and IDs the preview goes blank. If I am so foolish as to save these changes, the next time the editor loads C5 freezes until I uncheck that box. It sounds like such a good feature, but I can't use it because it causes the editor to freeze.