Having background issue on lines


Hope someone can help me, before I start I created a custom line renderer that works like when you replace the line it will change the marker start and marker end and so far it’s all working,

however when I already replace it to custom line when I am trying to connect it to other element,

the line seems to have diagonal background, please see image below

BUT when I connected it to the element the background is gone.

and when I save as SVG the background is showing up as well.

Thank you

Which versions of diagram-js / bpmn-js do you use?