Beamer frametitle unexpected behavior

Question

In beamer if some content follows the frame title in curly brackets, then the content will be also a part of the title. It happens only when the title is given without explicitly calling \frametitle.

Is it a bug or a feature? If the latter, why is it good?

See the difference between the three frames.

\documentclass{beamer}

\begin{document}

\begin{frame}\frametitle{Title} 
{content}
\end{frame}

\begin{frame}{Title} %Without calling \frametitle
{content}
\end{frame}

\begin{frame}{Title} %Only 
content
\end{frame}

\end{document}

Answer 1

According to the beamer documentation, the frame environment accepts the following arguments:

\begin{frame}<⟨overlay specification⟩>[<⟨default overlay specification⟩>][⟨options⟩]{⟨title⟩}{⟨subtitle⟩}

Therefore, {content} in your second slide is interpreted as the framesubtitle and

\begin{frame}{Title}
{contents}
\end{frame}

is actually equivalent to

\begin{frame}
\frametitle{Title}
\framesubtitle{contents}
\end{frame}

To overcome this, you can use the following:

\begin{frame}{Title}{}
{content}
\end{frame}