With setting the MidLabel of my customized GoLabeledLink to a GoPort I was able to link from this port. My problem is that the layout of the new link connected to this port is incorrect. All ‘regular’ links get layed out as I set them up (Bezier, and AdjustingStyle = Scale after resize).
When debugging, I found that the newly created link was of my custom type as expected and the style was set to Bezier. Still on the document it shows up as a straight line with only two selection handles when selected (resize impossible). 
Do you have a clou what is going on?
Thanks,
Angelika
If both ports connected by the Bezier style link have a spot that is GoObject.NoSpot (i.e. the FromPort’s FromSpot is NoSpot and the ToPort’s ToSpot is NoSpot), then GoLink.CalculateStroke will automatically make the link be a Bezier curve according to the GoLink.Curviness value.
So my guess is that the ports don’t both specify no link connection spot.
It is amayzing how you do this all the time!
Setting the FromSpot and ToSpot of the port to NoSpot did the job. It looks very nice by the way…
Thanks,
Angelika