Unbalanced nested quotation marks with [french]{babel} and csquotes

[AntoineGautierUL]

(I posted this here: tex.stackexchange.com)

I am using both [french]{babel} and csquotes. I get some unexpected behavior resulting in unbalanced quotation marks:

\enquote{Oui, mais \enquote{non}} yields « Oui, mais « non » (notice a single closing guillemet and wrong quotation marks at the nested level.

Using the babel \frquote command, things come out OK: \frquote{Oui, mais \frquote{non}} yields « Oui, mais "non" ».

Here is my test code:

\documentclass{article}
\usepackage[french=guillemets]{csquotes}
\usepackage[french]{babel}

\begin{document}
\enquote{Oui, mais \enquote{non}} (wrong)\hfill % « Oui, mais « non »
\frquote{Oui, mais \frquote{non}} (right).\\    % « Oui, mais "non" »
\end{document}

Would that be a bug? Thanks!