problem in eqnarray

Dear all,

I am experiencing a rather strange problem inside the eqnarray environment
(using texpower+pdfscreen). A \nonumber command seems necessary to
avoid an equation number to appear in the last line (where there is no
formula!) Below there code showing the problem.
How can I fix it without putting \nonumber in the line without formula?
Where am I wrong?

Many thanks for your help,
cheers,

vito


%%%%%%%%%%%%%%%%%%

\documentclass[12pt]{article}

\usepackage[screen,panelright,sectionbreak]{pdfscreen}

\margins{2ex}{2ex}{2ex}{2ex} \screensize{6.25in}{8in}

\usepackage[display,coloremph,colormath]{texpower}
\usepackage{tpslifonts}

\begin{document}

\section{section 1}

\begin{itemize}
    \item item1 \pause
\parstepwise
{%
\begin{eqnarray} %\nonumber
a & \step{\equiv} & \restep{b+c+d} \\
  & \step{=} & \restep{e+f+g} \\
                     %<==== Here \nonumber is necessary, otherwise.....
\end{eqnarray}
}%

    \item item2

\end{itemize}


\end{document}


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