Onslide en tabularx produce espacio vertical

Question

tengo un tabular en unbeamerpresentación de la cual quiero descubrir su contenido usando \onslide. Entabularx(o tabularcon una pcolumna) esto produce un peculiar espacio en blanco vertical en la Xcolumna. ¿Alguna idea sobre de dónde viene y/o cómo solucionarlo?

Aquí está el código que utilicé:

\begin{tabularx}{\textwidth}{|l|X|}
\hline
First line & A very long sentence that takes up more than one line because of its length\\
\onslide<2->{Second line} & \onslide<2->{A slightly longer sentence that takes up more than one line because of its length} \\
\hline
\end{tabularx}

O con una pcolumna:

\begin{tabular}{|l|p{0.7\textwidth}|}
\hline
First line & A very long sentence that takes up more than one line because of its length\\
\onslide<2->{Second line} & \onslide<2->{A slightly longer sentence that takes up more than one line because of its length} \\
\hline
\end{tabular}

Answer 1

Debes evitar poner las ofertas especiales del proyector (o cualquier oferta especial) al inicio de un parbox:

\documentclass{beamer}
\begin{document}
\begin{frame}
\begin{tabular}{|l|p{0.7\textwidth}|}
\hline
First line & A very long sentence that takes up more than one line because of its length\\
\onslide<2->{Second line} & \leavevmode\onslide<2->{A slightly longer sentence that takes up more than one line because of its length} \\
\hline
\end{tabular}
\end{frame}
\end{document}