How to diagnose what is changing a label?

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:


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,
Author = {Peter Wilson and Lars Madsen},
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}}

• Welcome to TeX.SX! Please help us to help you and add a minimal working example (MWE) that illustrates your problem. It will be much easier for us to reproduce your situation and find out what the issue is when we see compilable code, starting with \documentclass{...} and ending with \end{document}. – cfr Oct 10 '14 at 3:32

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