ofPath arc glitch

i wrote a simple script that draws an arc with a certain thickness. but for some positions i get this strange glitch with one vertex seemingly being point(0,0).

maybe i am doing something wrong with adding one arc to the next?

i am on OS X 10.10.5, OF 0.9.3

link to video: https://www.dropbox.com/s/7h0z9nr7bj089s8/Untitled.mov?dl=0

here is my code:

this seems to have fixed that

    ofPath inner_pLine;
    inner_pLine.setCircleResolution(200);
    
    inner_pLine.arc( 0, 0, _radius, _radius, _beginAngle, _endAngle);
    inner_pLine.arcNegative( 0, 0, _radius+_thickness, _radius+_thickness,_endAngle,_beginAngle);
    inner_pLine.close();

    inner_pLine.setColor(ofColor(255,0,0));
//    inner_pLine.setFillColor(ofColor(255,0,0));
//    inner_pLine.setFilled(true);
    inner_pLine.draw();
    
    
    float _midAngle = _beginAngle + (_endAngle-_beginAngle)/2;
    float x = _radius * cos(ofDegToRad(_midAngle));
    float y = _radius * sin(ofDegToRad(_midAngle));
    
    ofSetColor(255);
    ofDrawBitmapString("a", x, y);