Auto-hyphenation in Preview Panel?

I built an ebook last month, and everything went as usual. I started another yesterday, and I was astonished to see hyphenated words in the Preview Panel. In Code View, those words would be underlined in red for the portion that had been pushed onto the next line. I can make the hyphenation disappear if I change the width of the Preview Panel, but the red line remains.

Have I missed something? Is this a new option?

Sigil 0.9.6, Windows 7 Professional.