Undefined offset

I'm not really sure why this is happening, and there is only one search phrase that produces it, so rather than patch it I'm asking here if anyone has any thoughts. I'm also not sure what is relevant so I'm documenting the evidence only

My search is three words (though another three word search doesn't produce the error, and removing either of the clean_words doesn't produce the error either).
eg: alpha beta gamma

For one result (of about 30) clean_words matches twice in the same place. The match is a combination of the clean words joined by underscores
eg: $clean_words is (alpha, gamma) and the matches are (alpha_beta_gamma_delta, alpha_beta_gamma_delta).

The resulting section and section_length arrays have different lengths and therefore I get the undefined offset error when looping over the result. As the contents of section are two offsets in the same place if I array_unique() them I get arrays of the correct length and therefore no error.

From fuzzysearch.module

    409   asort($section);
    410   ksort($section_length);
    411   $section = array_unique(array_values($section));
    412   $section_length = array_values($section_length);

Is this something that we need a check for? Is there another (rarer) situation in which array_unique() won't be enough?