Re: grep.el regexp

[Richard M. Stallman]

    This approach has one problem: different rules in grep-regexp-alist
    are not mutually exclusive, so information from different regexps can
    appear in grep buffers from similar regexps.  In the worst case
    this can cause subsequent calls of `next-error' revisiting the
    same source line several times for each of separate regexps.

If that can happen, it is a bug in compile.el.
It should never find more than one match on any given line.