Overlay with nested itemize produce compile error

Hello!

Please consider this source file:

------BEGIN FILE-----------------------------
\documentclass[final,prettybox,slideColor,nototal,pdf]{prosper}

\begin{document}

\overlays{3}{%
\begin{slide}{Bug}
\fromSlide{1}{
\begin{itemize}
\item TTP
    \begin{itemize}
    \item primo
}
\fromSlide{2}{
    \item secondo
}
\fromSlide{1}{
    \end{itemize}
}
\fromSlide{2}{
\item Bob
    \begin{itemize}
    \item secundo
}
\fromSlide{3}{
    \item tertio
}
\fromSlide{2}{
    \end{itemize}
}
\fromSlide{1}{
\end{itemize}
}
\end{slide}}


\end{document}
-----END FILE---------------------------------

When LaTeXing this file it says:
-----BEGIN ERROR MESSAGE-------
! Extra }, or forgotten \endgroup.
\prosper@next ...@Verb {(1) BOL}{\ignorespaces #1}
                              \pst@Verb {(\curr@overlay ...
l.33 \end{slide}}
-----END ERROR MESSAGE-------

I suppose what is intended is clear, but just for sure:
First "slide":
- TTP
  - primo
Second "slide":
- TTP
  - primo
  - secundo
- Bob
  - secundo
Third "slide":
- TTP
  - primo
  - secundo
- Bob
  - secundo
  - tertio

The strangest thing is that pressing ENTER to bypass the error and
continue compiling will produce a correct pdf file (showing what I
intended to show).
Anyway this produces cascading errors on a long document, and it is
pretty annoying and strange.


Do you think this is a Prosper bug or am I misdoing something?

Thanks a lot.





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