bug of etoolbox and hyperref

\documentclass{article}
\usepackage{etoolbox}
% biblatex fails
\usepackage{biblatex}
\addbibresource{xampl.bib}
% If I load hyperref in \AtEndPreamble,
% biblatex's cite hyperlink didn't work
% bibtex's could work
% If I just load hyperref, both of them worked
\AtEndPreamble{\usepackage[colorlinks]{hyperref}}
% \usepackage[colorlinks]{hyperref}
\begin{document}
% test if hyperref works
\section{test}\label{sec}\ref{sec}

  \cite{article-full}
  \printbibliography
  % \bibliographystyle{plain}
  % \bibliography{xampl.bib}
\end{document}