How come decoration markings don't extend a TikZ picture's bounding box and how can I change this? Consider this example where the arrow markings are partially cropped.
\documentclass[tikz]{standalone}
\usetikzlibrary{decorations.markings}
\tikzset{
loop/.style 2 args={thick,decoration={markings,mark=at position {#1} with {\arrow{>},\node[anchor=\pgfdecoratedangle-90,font=\footnotesize,] {$p_{#2}$};}},postaction={decorate}}
}
\begin{document}
\begin{tikzpicture}[pin edge={shorten <=5*\lrad}]
\draw[loop/.list={{0.25}{1},{0.75}{2}}] (0,0) circle (1);
\end{tikzpicture}
\end{document}