Odd symbol: hyphenation suppression?

[Steve Rickaby]

I am working on a book in which some letter pairs are underlined when 'view symbols' is enabled. I don't recall having noticed this symbol before, so I looked it up, and the user guide suggests that it indicates hyphenation suppression [presumably manually applied?]

What strikes me as odd is that the underline symbol is removed neither by retyping the characters nor by applying 'default para font' to the word in question. If I copy/paste a word in which this underline symbol occurs into, say, the 'correction' box of the spell checker, it appears prefixed by a backslash underscore pair. Clicking 'show hyphenation' shows that the word in question appears to be set up to hyphenate as would be expected.

Can anyone tell me what is going on here, and whether these underlined letter pairs are really anything to do with hyphenation, and if not, what?

-- 
Steve