too much vertical space between text and an equation if text line is full

[Mo-Gul]

TeXing

\documentclass[
    fleqn,
        ]{article}
\usepackage{amsmath}
\usepackage{hyperref}
\begin{document}

Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod
tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
volu.
%
    \begin{equation}
        a = b
    \end{equation}
%
Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit
lobortis nisl ut aliquip ex ea commodo consequat. Duis autem vel eum iriure
\dots

\end{document}

gives

As you can see the vertical space between the text and the equation is too large.

Comment either fleqn, one of the \usepackages or the "volu" text line and the vertical space is "normal" again.

Is this a bug or a feature?

[u-fischer]

As a work-around use volu.% to suppress the final space.