It looks like the plugin subs the special characters out with HTML entities. Which characters were you attempting to add into the content?
Hey, while not actually being the developer, I can probably provide some insight here.
Currently the plugin is only cleaning data in the standard WordPress post content. This means that custom fields being generated via Advanced Custom Fields, Visual Editor, or any other secondary/tertiary content additions will not be cleaned.
I’m sure it’s being worked on, but I don’t know when that will be; from my understanding, it’s a far more involved process to scrub custom field data.
