[Tex/LaTex] BibTeX bibliography suddenly broken

Question

My sample document looks like this

\documentclass{article}

\title{Demo Bibtex}
\author{John Smith}

\begin{document}
\maketitle

Some claim \cite{velikonja2015asymmetric}.

\bibliographystyle{apacite}
\bibliography{References}
\end{document}

My bib file (References.bib) is located in the same folder and looks like this:

@article{velikonja2015asymmetric,
title={On asymmetric shape of electric double layer capacitance curve},
author={Velikonja, Alja{\v{z}} and Kralj-Igli{\v{c}}, Veronika and 
Igli{\v{c}}, Ale{\v{s}}},
journal={Int. J. Electrochem. Sci},
volume={10},
pages={1--7},
year={2015}
}

The resulting document looks broken:

Like everything in it is counted twice. Help much appreciated.

Answer 1

If I simply use class apa instead of article I can compile the code and bib entry without error message.

Try the following MWE (package filecontents is only used to get a compiling MWE with TeX code and bib file):

\RequirePackage{filecontents}
\begin{filecontents}{\jobname.bib}
@article{velikonja2015asymmetric,
  title={On asymmetric shape of electric double layer capacitance curve},
  author={Velikonja, Alja{\v{z}} and Kralj-Igli{\v{c}}, Veronika and 
          Igli{\v{c}}, Ale{\v{s}}},
  journal={Int. J. Electrochem. Sci},
  volume={10},
  pages={1--7},
  year={2015}
}
\end{filecontents}


\documentclass{apa} % article

\title{Demo Bibtex}
\author{John Smith}

\begin{document}
\maketitle

Some claim \cite{velikonja2015asymmetric}.

\bibliographystyle{apacite}
\bibliography{\jobname}
\end{document}

and the resulting pdf:

EDIT:

With class report and biblatex with biber:

\RequirePackage{filecontents}
\begin{filecontents}{\jobname.bib}
@article{velikonja2015asymmetric,
  title={On asymmetric shape of electric double layer capacitance curve},
  author={Velikonja, Alja{\v{z}} and Kralj-Igli{\v{c}}, Veronika and 
          Igli{\v{c}}, Ale{\v{s}}},
  journal={Int. J. Electrochem. Sci},
  volume={10},
  pages={1--7},
  year={2015},
}
\end{filecontents}


\documentclass{report} % article

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english]{babel}

\usepackage{csquotes}
\usepackage[%
  backend=biber,
  style = authoryear,
]{biblatex}
\addbibresource{\jobname.bib}

\title{Demo Bibtex}
\author{John Smith}

\begin{document}
\maketitle

Some claim \cite{velikonja2015asymmetric}.

\printbibliography
\end{document}

and the result: