Strange white line with \lstnewenvironment

Strange white line with \lstnewenvironment

I'm trying to write a \lstnewenvironment for my LaTeX class but I have a strange behaviour.
Here's my code :
\lstnewenvironment{console} {
   \lstset {
      basicstyle=\color{lightgrey}\scriptsize\ttfamily,
      backgroundcolor=\color{black},
      breaklines=true,
      numberstyle=\scriptsize,
      columns=flexible,
      keepspaces=true,
  }
}{}
And here's the result :

Do you have any idea what I'm doing wrong ?
Thanks!
EDIT:
I only see this behaviour in Preview.app on Mac OS but not in Chrome's pdf viewer!