The following code, and possibly related code, would need to be modified in search_functions.php to cut on a space rather than take a substring:
Code:
// v.1.8.7
$extract_content = substr($extract_content,$first_bold_spot,max(SNIPPET_DISPLAY_LENGTH, 2 * strlen($query_string)));
// v.1.8.8 RC1
$extract_content = mb_substr($extract_content,$first_bold_spot,$length_of_snip);