Onslide in Tabularx erzeugt vertikalen Raum

Question

Ich habe eine Tabelle in einembeamerPräsentation, deren Inhalt ich mit enthüllen möchte \onslide. Intabularx(oder in tabulareiner p-Spalte) erzeugt dies einen eigenartigen vertikalen Leerraum in der X-Spalte. Irgendwelche Ideen, woher das kommt und/oder wie man es umgehen kann?

Hier ist der Code, den ich verwendet habe:

\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}

Oder mit einer p-Spalte:

\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

Sie müssen vermeiden, die Beamer-Specials (oder irgendwelche Specials) an den Anfang einer Parbox zu setzen:

\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}