font-lock: doesn't colour non-ascii dash in string correctly

[Chris Moore]

I have a string in a C file:

  "hello­world"

Both quotes and all the letters are coloured in the usual string face, an 
orange kind of colour, but the dash is cyan.  It's inside a string, so why 
isn't it "string coloured"?

Here's the output of 'od' on the file:

    $ od -tc /tmp/man.el
    0000000   "   h   e   l   l   o 255   w   o   r   l   d   "  \n
    0000016

    $ od -tx1 /tmp/man.el
    0000000 22 68 65 6c 6c 6f ad 77 6f 72 6c 64 22 0a
    0000016

describe-char tells me it's:

       character: ­ (2221, #o4255, #x8ad, U+00AD)
         charset: latin-iso8859-1
                (Right-Hand Part of Latin Alphabet 1 (ISO/IEC 8859-1): 
ISO-IR-100.)
      code point: #x2D
          syntax: _     which means: symbol
        category: l:Latin
     buffer code: #x81 #xAD
       file code: #xAD (encoded by coding system windows-1250-unix)
         display: by this font (glyph code)
       -Misc-Fixed-Medium-R-Normal--20-200-75-75-C-100-ISO8859-1 (#xAD)
  hardcoded face: escape-glyph

Chris.