How to diagnose what is changing a label?

Question

I was getting this only last warning, no matter how many times I rerun my .tex file:

LaTeX Warning: Label(s) may have changed. Rerun to get cross-references right.

Then I saw this question and the answer's code helped me to find what was changing, in my case, my only reference in a .bib file:

label memoir changed:
macro:->\hyper@@link [cite]{}{cite.memoir\@extra@b@citeb }{\@safe@activesfalse
Wilson e Madsen 2010}
macro:->\hyper@@link [cite]{}{cite.memoir}{Wilson e Madsen 2010}

Any ideas on what could be causing this or how to track the problem?

Edit:

Here is a MWE. I am using the abntex2 package (included in MiKTeX, they are Brazilian rules for documents, maybe the bug is here) and my enviroment is: Windows + MiKTeX + Texmaker editor. My compile sequence is PdfLaTeX + Bib(la)tex + PdfLaTeX + PdfLaTeX.

\documentclass[english,brazil]{abntex2}

\RequirePackage[alf]{abntex2cite}

% This code is just for diagnosis (see the question)
\makeatletter
\def\@testdef #1#2#3{%
  \def\reserved@a{#3}\expandafter \ifx \csname #1@#2\endcsname
 \reserved@a  \else
\typeout{^^Jlabel #2 changed:^^J%
\meaning\reserved@a^^J%
\expandafter\meaning\csname #1@#2\endcsname^^J}%
\@tempswatrue \fi}
%

\begin{document}
\chapter{test}
\citeonline{memoir}
\bibliography{referencias}
\end{document}

My referencias.bib contains:

@manual{memoir,
    Address = {Normandy Park, WA},
    Author = {Peter Wilson and Lars Madsen},
    Date-Added = {2013-01-09 10:37:50 +0000},
    Date-Modified = {2013-03-21 13:23:25 +0000},
    Organization = {The Herries Press},
    Title = {The Memoir Class for Configurable Typesetting - User Guide},
    Url = {http://mirrors.ctan.org/macros/latex/contrib/memoir/memman.pdf},
    Urlaccessdate = {19 dez. 2012},
    Year = {2010},
    Bdsk-Url-1 = {http://ctan.tche.br/macros/latex/contrib/memoir/memman.pdf}}

Answer 1

I had the same problem with the abntex2 class. The reason for the warning seems to be that abntex2cite.sty is redefining the \bibcite command from hyperref. I fixed the warning by commenting the extra \bibcite definition in abntex2cite.sty:

(line 628:)

\ifthenelse{\boolean{ABNThyperref}}{%
%\renewcommand{\bibcite}[2]{%                            comment  this line
% \@newl@bel{b}{#1}{\hyper@@link[cite]{}{cite.#1}{#2}}}% comment  this line
\newcommand{\bibciteEXPL}[2]{%
 \@newl@bel{b}{#1++EXPL}{\hyper@@link[cite]{}{cite.#1}{#2}}}%
\newcommand{\bibciteIMPL}[2]{%
 \@newl@bel{b}{#1++IMPL}{\hyper@@link[cite]{}{cite.#1}{#2}}}%
\newcommand{\bibciteYEAR}[2]{%
 \@newl@bel{b}{#1++YEAR}{\hyper@@link[cite]{}{cite.#1}{#2}}}%
}{} 

I did not notice any difference in the generated pdf file.