Latex Beamer: Prevent vertical text overflow for multi column or minipages

Question

To get a feeling for the sizes of the area reserved for text in different latex beamer layouts (themes) I am filling the text area with \blindtext. This works for simple frames with single column content. But when using multi column environments vertical text overflow appears. This happens for both, the columns and the minipage environments.

In addition to the question stated in the title, it would be great if someone knows a way to visualize the maximum space reserved for different contents like titles, text, headers, footers, etc. for different themes.

MWE:

\documentclass{beamer}
\usepackage{blindtext}
\usetheme{Frankfurt}
%#############################################################
\begin{document}
\begin{frame}
\blindtext
\end{frame}

% Two columns using minipage
\begin{frame}
\begin{minipage}{0.5\textwidth}
\blindtext
\end{minipage}%
\begin{minipage}{0.5\textwidth}
\blindtext
\end{minipage}  
\end{frame}

% Two columns using columns
\begin{frame}
\begin{columns}[onlytextwidth]
\begin{column}{.5\textwidth}
\blindtext
\end{column}
\begin{column}{.5\textwidth}
\blindtext
\end{column}

\end{columns}
\end{frame}

\end{document}

The three output frames from the above MWE are shown below:

1. frame: simple frame output as expected
2. frame: Two columns using minipage environment, vertical text overflow
3. frame: Two columns using columns environment, vertical text overflow

Answer 1

All the space which is occupied in your example is the available space. It is in the responsibility of the user that the content will fit onto the frame, if too much text is put on a frame, it will simply overflow at the bottom (with the exception of frames using allowframebreak, but this should only be used as emergency solution, for example for the bibliography).

If you would use a longer text in your one column example (e.g. \blindtext \blindtext), you would see the same effect.

If you want a blindtext with more flexible lenght for demonstration purpose of your theme, I suggest the lipsum package instead, as this allows to select which paragraph of the sample text should be used:

\documentclass{beamer}
\usetheme{Frankfurt}

\usepackage{lipsum}
%#############################################################
\begin{document}
\begin{frame}
\lipsum[21]
\end{frame}

% Two columns using minipage
\begin{frame}
\begin{minipage}{0.48\textwidth}
\lipsum[11]
\end{minipage}%
\hfill
\begin{minipage}{0.48\textwidth}
\lipsum[11]
\end{minipage}  
\end{frame}

% Two columns using columns
\begin{frame}
\begin{columns}[onlytextwidth]
\begin{column}{.48\textwidth}
\lipsum[11]
\end{column}
\begin{column}{.48\textwidth}
\lipsum[11]
\end{column}

\end{columns}
\end{frame}

\end{document}