HTMLCleaner defines the style-tag as being allowed both in the HTML body and head for HTML5. The current version of the HTML5 standard says that the style element cannot be used in the body, though. It was only allowed if the scoped attribute was present apparently, and the scoped attribute is deprecated according to MDN and not supported by the current version of any browser. Therefore, I think HTMLCleaner also shouldn't allow style-tags in the HTML body.
Fixed; will be in 2.28 release