Fails when multiple diagrams are present

[Mk-arc]

\documentclass{scrartcl}
\usepackage{graphics}
\usepackage{epstopdf}
\epstopdfDeclareGraphicsRule{.svg}{pdf}{.pdf}{
  inkscape -z --file=#1 --export-pdf=\OutputFile
}
\usepackage[output=svg]{plantuml}
\begin{document}
\begin{plantuml}
@startuml
class Car

Driver - Car : drives >
Car *- Wheel : have 4 >
Car -- Person : < owns
@enduml
\end{plantuml}

\begin{plantuml}
@startuml
class Bus
@enduml
\end{plantuml}

\end{document}

Produces wrong output as soon as 2 diagrams exist. The output file name seems to be always the same. Thus, the second diagram overwrites the first one.

[Mk-arc]

Note: It works well when not using the svg step. E.g. just using plantuml via:

\usepackage{plantuml}