A = \left( ... \right) always right justified

[ianhbell]

With this MWE, how can I get the broken lines in the parentheses to be left justified?

\documentclass[12pt]{article}
\usepackage{breqn}
\begin{document}
\begin{dmath}
a = \left(b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b+b \right)
\end{dmath}
\end{document}