Created attachment 236737 [details]
Screenshot showing both problems, non highlighted text and highlighted until the end of the paragraph.
Epiphany 3.12.1 and WebKit 2.4.4
This bug is not reproducible in a predictable way.
Sometimes, when searching in a page, the highlighting of the text to be found is not working in some of the occurrences while in others it is selecting from the found text until the end of the paragraph.
Usually, when navigating through the found occurrences, the navigation works correctly and the selections on the "actual" found text works as well. Often, too, when re-starting the search from the beginning of the page after having gone to the bottom corrects the malfunctioning highlighting.