no line breaking in mdframed with geometry package

Question

I am trying to include a python code (within a colored mdframed box) into my tex file. However, I noticed that when I use the geometry package simultaniously with mdframed and fancyhdr, two things happen:

1) automatic line breaking within mdframed boxes doesn't work anymore 2) the top and bottom margins are set to a value around 1cm (no matter what value I set)

When I remove the geometry package, the line breaking works, but the (default) margins are again way too large.

Here my code:

\documentclass[12pt, a4paper, titlepage]{article}

\usepackage[dvipsnames]{xcolor}
\usepackage[ngerman]{babel}

\usepackage[margin=2.54cm]{geometry}
\usepackage{fancyhdr}
\usepackage{mdframed}

\pagestyle{fancy}

\newcommand{\gbx}[1]{
\begin{mdframed}[backgroundcolor=black!20, leftmargin=0, rightmargin=0, innertopmargin=10pt, innerbottommargin=10pt, topline=false, bottomline=false, rightline=false, leftline=false]
#1
\end{mdframed}
}

\begin{document}

\gbx{\texttt{import numpy as np\\
import matplotlib.pyplot as plt\\\\
verteilung = np.random.normal(0., 1., 1000000)\\
bins = len(verteilung)/15000\\\\
fig = plt.figure()\\
ax = fig.add\_subplot(111)\\
plt.hist(verteilung, bins = bins, normed = 1, color = 'blue', label = 'Zufallswerte')\\
plt.xlabel('Wert')\\
plt.ylabel('Anzahl')\\
ax.annotate('Maximum', xy = (0, 0.4), xytext = (-0.75, 0.42))\\
plt.legend()\\
plt.grid()\\
plt.savefig('histo.svg', format='svg', dpi=1000)\\
plt.show()
}}

\end{document}

Now does anyone have a solution for this? How can I get automatic line breaking AND a 2.54cm margin (while using fancyhdr)?

Thanks a lot!

PS: the anysize package (used to set the margins) produces the same output.