It seems my previous mistake killed my credibility. Well...
This is a plain and basic way to
reproduce this faulty display (though, I'm sure it's NOT the only one)
Open the above EPUB with Sigil 0.4 beta.
Open the style sheet named
styles1.css
Suppress the last item (about
p { text-align:justify; })
Save and close the EPUB
Open again: here is the faulty display.
This happens with the button Html Tidy on and off.