JDiagram version 4.1.1 contains the following new features and fixed bugs:

Improved arrowhead rendering
~ arrowheads are rendered as a single path when possible and several arrowhead Shape definitions have been changed to implement mitered joints when HeadPen is set to a thick pen.
~ the point where end segments connect to arrowheads can be specified via the Shape.LinkSegmentInset property. Shape definitions from the ArrowHeads class set it to suitable default value. This allows using transparent or semi-transparent brushes without seeing the link line drawn behind arrowheads.
~ arrowhead shadows are no longer filled if the link's EffectiveBrush is null or fully transparent.
~ IntermediateShape is now also rendered for Bezier links.

Miscellaneous
~ Set the LinkLabel.Brush property to fill the background of link labels.
~ Multiple-resize of rotated nodes fixed to apply same offsets in nodes' local coordinate system.
~ Fixed a bug where setting the CaptionBackBrush property of containers would hide the caption-bar borders.

If anyone is interested in trying the beta version, please download this archive containing the updated jar file:
https://mindfusion.eu/_beta/jdiag.4.1.1.zip

Any comments, questions and general feedback are welcome.