Custom Line End Line Ends rotation on arc

[Caveatrob]

I created a custom line end after being frustrated that there was no
way to "fill" an arrowhead on an existing line end easily.

It works fine on straight lines, however on arcs it is slightly tilted
and doesn't align nicely like it does with the existing ends.

I set my pin to the arrowhead point (my line end, simply an arrowhead
pointing to the right with a filled head) and it still doesn't work
right on arcs.