Unwanted White Lines in listings environment

Unwanted White Lines in listings environment

\documentclass{article}
\usepackage{listings}
\usepackage{color}
\begin{document}
\definecolor{light-gray}{gray}{0.95}
\lstset{basicstyle=\ttfamily\footnotesize,
backgroundcolor=\color{light-gray}, xleftmargin=0.7cm,
frame=tlbr, framesep=0.2cm, framerule=0pt,
}
\begin{lstlisting}[mathescape]
k = $\lfloor (10\log n \cdot \log\log n)^{1/3} \rfloor$;
k = $\lfloor (4\log n \cdot \log n)^{1/3} \rfloor$;
\end{lstlisting}
\end{document}
produces

An answer to a similar question said that "this line is just an artifact
of the viewer". But this line appears in two viewers and various zoom
steps. On top of that, one can clearly see that the 1/3 overlaps with the
white line. So I do not accept it as a mere artifact anymore.
How could this problem be approached? Is it possible to somehow put
another grey layer underneath the lstlisting environment which would "eat
up" any white lines?