image_filter_attr_value deletes hyphens

css classes can use hyphens, e.g. "inline-image-right". Image Filter deletes the hyphens and renders a class attribute incorrectly. I changed the IMAGE_FILTER_WORD regex from:
return preg_replace("/\D/", '', $text);
to
return preg_replace("/[^\w-]/", '', $text);
This fixes the problem for me.