\end{center} but still centering

Question

I am centering a text:

\documentclass{memoir}

\renewcommand{\partpageend}{} %% can write after part title
\usepackage{graphicx}



\renewcommand{\beforepartskip}{% added <<<<<<<<<<<<<<<<<
        \centering
        \includegraphics[width=0.4\linewidth]{example-image} 
        \par\vfill
}

\begin{document}
    
    \part{This is a title}
    
    \begin{center}
        \textbf{This text is being centered and that's what I want.}
        \vfill
    \end{center}
    
    \newpage
    
This text should not be centered anymore.
This text should not be centered anymore.
This text should not be centered anymore.
This text should not be centered anymore.
This text should not be centered anymore.
This text should not be centered anymore.
This text should not be centered anymore.
This text should not be centered anymore.

\end{document}

But after \end{center} everything else is still being centered.

Thank you in advance.

Answer 1

As has already been noted by @HeikoTheißen in a comment, the centering issue you're experiencing arises because the \centering command in the definition of \beforepartskip is not in a (TeX) group and hence persists. The fact that the document also features, separately, a center environment, is immaterial.

One way to fix this is to replace

\renewcommand{\beforepartskip}{% added <<<<<<<<<<<<<<<<<
        \centering
        \includegraphics[width=0.4\linewidth]{example-image} 
        \par}\vfill
}

with

\renewcommand{\beforepartskip}{{% added <<<<<<<<<<<<<<<<<
        \centering
        \includegraphics[width=0.4\linewidth]{example-image}
        \par}\vfill
}

Can you spot the extra instances of { and }?