ImDrawList.path_* methods sometimes adding arrowheads?

[bgribble]

I am doing some custom drawing inside a imgui_node_editor node to draw a shape that includes arcs. ImDrawList.path_arc_to seems to be the only way to draw a partial circle, so I am using this code snippet to draw a shape and stroke it:

        outer_radius = self.width / 2
        inner_radius = self.width / 6 

        draw_list.path_arc_to(
            [self.position_x + self.width / 2,
             self.position_y + self.height / 2],
            outer_radius,
            self.THETA_MIN,
            2*math.pi + self.THETA_MAX,
            35 
        )
        draw_list.path_line_to(
            [
                self.position_x + self.width / 2 + inner_radius*math.cos(self.THETA_MAX),
                self.position_y + self.height / 2 + inner_radius*math.sin(self.THETA_MAX)
            ]
        )
        draw_list.path_arc_to(
            [self.position_x + self.width / 2,
             self.position_y + self.height / 2],
            inner_radius,
            self.THETA_MAX,
            self.THETA_MIN - 2*math.pi,
            35 
        )
        draw_list.path_stroke(
            ColorDB().backend.im_col32(color),
            imgui.ImDrawFlags_.closed,
            1.0
        )

The rendered shape is as expected, except that there is an arrowhead in place of the path_line_to segment. While trying different things, I have occasionally seen arrowheads on arc segments as well. I don't understand what is causing them, and I can't find any hints in the imgui code. Any thoughts?

Screenshot showing the issue ... the arrowhead is on the right straight edge of the "donut with a pie piece out" shape that is drawn by the above code. In the code, THETA_MIN is the angle of the left side and THETA_MAX is the angle of the right, so the arrow is on the path_line_to segment. The other straight segment comes automatically because the path_stroke has closed set.

Any ideas?