Package Listings Warning: Text dropped after begin of listing on input line ...

documentclass{article}

usepackage{listings}       % Source code listings
usepackage{enumitem}
usepackage{mdframed}

% Define questions environment with framed question
newcommand{questionlabel}{Question }
newcommand{restorequestionlabel}{renewcommand{questionlabel}{Question }}
newcommand{setquestionlabel}[1]{renewcommand{questionlabel}{#1 }}
newlist{questions}{enumerate}{4}
setlist[questions]{align=left,ref=questionlabelarabic*,label=textbf{questionlabelarabic*.},wide}
newcommand{itembr}{needspace{10baselineskip}itemmbox{}}
newcommand{question}[1]{itembrbegin{mdframed}#1end{mdframed}}

begin{document}

begin{questions}
question{
It works outside the question frame
}
begin{lstlisting}[language=C]
int* p = (int*) malloc(100 * sizeof(int));
int i;
for(i = 0; i < 100; i++) {
    p[i] = i;
}
end{lstlisting}

question{And it works inside a separate mdframed}
begin{mdframed}
begin{lstlisting}[language=C]
int* p = (int*) malloc(100 * sizeof(int));
int i;
for(i = 0; i < 100; i++) {
    p[i] = i;
}
end{lstlisting}
end{mdframed}

item
begin{lstlisting}[language=C]
int* p = (int*) malloc(100 * sizeof(int));
int i;
for(i = 0; i < 100; i++) {
    p[i] = i;
}
end{lstlisting}

Also works with $backslash$item

question{
What about inside the question?

%begin{lstlisting}[language=C]
%int* p = (int*) malloc(100 * sizeof(int));
%int i;
%for(i = 0; i < 100; i++)
%    p[i] = i;
%end{lstlisting}

Package Listings Warning: Text dropped after begin of listing on input line ...
}

end{questions}

end{document}