Inconsistent horizontal width of mdframed with only display math content

Question

Update 2012-03-09: With an version of mdframed updated today, this is now fixed in the package and no longer requires the workaround provided below.

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In Excess vertical space in mdframed ending with display math environment, I had wrapped the contents on mdframed within a minipage and had intended to file this as a separate question, as I believe that the minipage wrapper should not be necessary. Without this wrapper, if the content contains only display math, the width is not the full \linewidth.

Here is a snippet of the output showing the inconsistent output for the case of display math in red. Note that the output is fine if the frame has a title, but without the frame the width is not consistent:

Questions:

• Is there a mdframed setting to adjust this? If not, is there any better way to get the desired behavior other than using a minipage?
• Is this a bug with mdframed, or a feature?

Note:

• The code below is adapted from mdframed: Put a line below the frame title and give it a shaded background.
• Uncommenting the \begin{minipage} and \end{minipage} produces what I believe is the correct result (to be consistent with the first two cases).

Code:

\documentclass{article}
\usepackage{showframe}
\usepackage{amsmath}
\usepackage[framemethod=TikZ]{mdframed}
\newenvironment{Frame}[1][]{%
    \begin{mdframed}[%
        frametitle={#1},
        skipabove=\baselineskip plus 2pt minus 1pt,
        skipbelow=\baselineskip plus 2pt minus 1pt,
        linewidth=0.5pt,
        frametitlerule=true,
        frametitlebackgroundcolor=gray!30
    ]%
    %\begin{minipage}{\linewidth}%  this should not be necessary??
}{%
    %\end{minipage}%
    \end{mdframed}
}
\begin{document}\noindent
Text
\begin{Frame}[with Title]
    Text
\end{Frame}
Text
\begin{Frame}% no Title
    Text
\end{Frame}
Text
\begin{Frame}[Einstein]
    \begin{align}
        e & = mc^2
    \end{align}
\end{Frame}
Text
\begin{Frame}\color{red}% no Title
    \begin{align}
        e & = mc^2
    \end{align}
\end{Frame}
Text
\begin{Frame}\color{red}% no Title
    \begin{align}
        e  &= mc^2\
        F  &= ma
    \end{align}
\end{Frame}
Text
\begin{Frame}\color{red}% no Title
    [
        e  = mc^2
    ]
\end{Frame}
\end{document}

Answer 1

I wouldn't use a minipage as that stops breaking the frame, which is, presumably the main point of the mdframed frame, Between the tikz and the German I'm not sure whether it's a bug or (like minipage) it is a feature. A standard LaTeX minipage will similarly ignore its requested length and just use the natural length of its content if its content is just vertical material. (This is documented as working if you put a tabbing in minipage but it is generally true. So I'd just force the width by putting a rule in:

\newenvironment{Frame}[1][]{%
    \begin{mdframed}[%
        frametitle={#1},
        skipabove=\baselineskip plus 2pt minus 1pt,
        skipbelow=\baselineskip plus 2pt minus 1pt,
        linewidth=0.5pt,
        frametitlerule=true,
        frametitlebackgroundcolor=gray!30
    ]%
    \hrule height0pt width\hsize\relax%<<<<<<<<<<<<<<FORCE WIDTH
    %\begin{minipage}{\linewidth}%  this should not be necessary??
}{%
    %\end{minipage}%
    \end{mdframed}
}