Activity Diagram Split and Swimlane minor layout bug

Question

I wanted to model an activity where a step is done in parallel by different actors. For this, I created an activity diagram with split and swimlanes, see minimal example below and link to the online server.

For some reason, the line that goes to W1 does not go left and down, but first goes a bit upwards, then left, then down. This leads to an unwanted square shape. I would expect that the arrows to W1, W2 and W3 start at the same horizontal line and only go downwards and to the side.

Test case: http://www.plantuml.com/plantuml/uml/SoWkIImgAStDuQfnhE42So2iWfpC4Yu58B0ADxJcgd622YaafYTcva4bZAon21fRSwNcfIY09O06vXTmEG3vG1i0

@startuml
start
|A|
split
    :W1;
|B|
split again
    :W2;
split again
    :W3;
end split
stop
@enduml