Loop in disconnected diagram not showing with tikz-feynman

Question

I am trying to make the following disconnected diagram using tikz-feynman

My attempt:

\documentclass{standalone}
\usepackage[compat=1.1.0]{tikz-feynman}
\begin{document}
    \begin{tikzpicture}
        \begin{feynman}[large]
            \vertex [anchor = north](a) {$t'$};
            \vertex [anchor = north, right = of a] (b) {$t$};
            \vertex (d) at ($(a)!0.5!(b)$);
            \vertex [small, dot, below = of d] (c) {};
            \diagram*{(a) --[fermion] (b),
                (c) -- [fermion,loop, in = 45, out  = 135, min distance = 1cm] (c) -- [fermion,loop, out = -45, in  = -135, min distance = 1cm] (c)};
        \end{feynman}
    \end{tikzpicture}   
\end{document}

This produces the following output

As you can see, the fermion loops do not show up! Why is that, and how can i fix this?

Thank you.

Answer 1

Workaround Solution

I found a way to do this, but I don't really like it, so improvements are welcome.

By creating a new vertex (d) on the same position as (c), it all of a sudden works.

Code

\documentclass{standalone}
\usepackage[compat=1.1.0]{tikz-feynman}
\begin{document}
    \begin{tikzpicture}
        \begin{feynman}[large]
            \vertex [anchor = north](a) {$t'$};
            \vertex [anchor = north, right = of a] (b) {$t$};
            \vertex (d) at ($(a)!0.5!(b)$);
            \vertex [small, dot, below = of d] (c) {};
            \vertex (d) at (c);
            \diagram*{(a) --[fermion] (b),
                (c) -- [fermion,loop, in = 45, out  = 135, min distance = 1cm] (d) -- [fermion,loop, out = -45, in  = -135, min distance = 1cm] (c)};
        \end{feynman}
    \end{tikzpicture}   
\end{document}

Output