Consider the following MWE
\documentclass[11pt,oneside]{memoir}
\usepackage{breqn}
\usepackage{hyperref}
\begin{document}
\mainmatter
\begin{dmath}\label{eq:1}
1 + 1 = 2,
\end{dmath}
\newpage
\begin{dmath}\label{eq:2}
1 + 1 = 2,
\end{dmath}
\newpage
\ref{eq:2}
\end{document}
where after running the document through pdflatex a couple of times we find that clicking on the reference to equation 2 actually takes us to equation 1. If the dmath blocks are replaced with regular equations everything works as expected.
memoir
.