LaTeX minipage environment cuts off math text

Question

I am having an issue with a project in LaTeX and would be very happy to find help here.

I am writing a book for my math class. As with many scripts, the content consists of theorems and related things. The definition of my theorem environments seems to be a little bit off, which results in the following problem:

Inspired by an artice on this website, I have defined my theorem environments as follows

\usepackage{ifmtarg}        % http://ctan.org/pkg/ifmtarg
\usepackage{xifthen}        % http://ctan.org/pkg/xifthen
\usepackage{environ}        % http://ctan.org/pkg/environ
\usepackage{multido}        % http://ctan.org/pkg/multido

\makeatletter%

% top theorem decoration
\newcommand{\theoremhang}[1]{
  \begingroup%
  \setlength{\unitlength}{.005\linewidth}% \linewidth/200
    \begin{picture}(0,0)(1.5,0)%
      \linethickness{1.5pt} \color{#1!50}%
      \put(-3,2){\line(1,0){206}}% Top line
      \multido{\iA=2+-1,\iB=50+-10}{5}{% Top hangs
        \color{#1!\iB}%
        \put(-3,\iA){\line(0,-1){1}}% Top left hang
        \put(203,\iA){\line(0,-1){1}}% Top right hang
      }%
    \end{picture}%
  \endgroup%
}%

% bottom theorem decoration
\newcommand{\theoremhung}[1]{
  \nobreak
  \begingroup%
    \setlength{\unitlength}{.005\linewidth}% \linewidth/200
    \begin{picture}(0,0)(1.5,0)%
      \linethickness{1.5pt} \color{#1!50}%
      \put(-3,0){\line(1,0){206}}% Bottom line
      \multido{\iA=0+1,\iB=50+-10}{5}{% Bottom hangs
        \color{#1!\iB}%
        \put(-3,\iA){\line(0,1){1}}% Bottom left hang
        \put(203,\iA){\line(0,1){1}}% Bottom right hang
      }%
    \end{picture}%
  \endgroup%
}%

%Theorem counter
\newcounter{theorem}                %Counter for theorems
\counterwithin{theorem}{chapter}    %Resets counter for each chapter
\renewcommand{\thetheorem}{\arabic{theorem}}

With the environment "Satz" as

\NewEnviron{satz}[1][]{%
    \par\noindent\theoremhang{black}\par\nobreak\noindent%\addvspace{-.5ex}
    \refstepcounter{theorem}\postdisplaypenalty=10000 %
    {\sffamily\bfseries\upshape Satz \thechapter.\thetheorem\@ifnotmtarg{#1}{\ (#1)}}\ \ \itshape\ignorespaces%
    \label{\thechapter.\thetheorem}\label{#1}
    \BODY % Typeset theorem body/content
    \par\addvspace{-1ex}\nobreak\noindent\theoremhung{black}\par\addvspace{.4ex}%
}

Could anybody help me resolve this issue? I wish to use these theorem environments and not the onces available with packages.