From: Ralf Angeli <address@hidden>
Frankly, I don't know it. I tried to find out what happens by
debugging involved functions but don't have time to do this
thoroughly. I checked with the RefTeX version included in CVS Emacs
and with a simple file like
\documentclass{article}
\begin{document}
\begin{equation}
\label{eq:1}
\end{equation}
\begin{lem}
\label{lem:1}
\end{lem}
\end{document}
and saw that "lem:1" shows up in `reftex-docstruct-symbol-1' (an
undocumented internal variable) with an "s" indicator, whereas "eq:1"
shows up with "e". So if you use `s' as the label type you will see
the "lem:1" label. I don't know why. It's probably best you ask
Carsten Dominik, the author of RefTeX, about the issue.