Re: highlight failed part of isearch input

[Richard Stallman]

    There is one inconsistence: when incrementally adding characters to the
    search string it highlights one part (only failed) of the search string,
    but when repeating the search with the same string from the search ring,
    it highlights the whole string.  This is a minor inconsistence, and can
    be tolerated if unavoidable.

I think that is correct behavior.  When you repeat the search, and
that fails, what failed is the whole string.