Possible Duplicate:
mdframed nested frametitle bug
This issue is fixed in version 1.6b
mdframed at github
It seems as if the frame title used in the mdframed environment can only have one value, which is problematic if the mdframes are nested.
For example, if I specify the title of an mdframe to as frametitle={Outer Title}, and then nest another mdframe within this with frametitle={Inner Title}, the output I get is:

Code:
\documentclass{article}
\usepackage[paperwidth=5.0cm]{geometry}% makes output image more palatable for TeX.SE
\usepackage{mdframed}
\begin{document}
\begin{mdframed}[frametitle={Outer Title}]
\begin{mdframed}[frametitle={Inner Title}]
\end{mdframed}
\end{mdframed}
\end{document}