ofFbo drawing order inside setup()

Hi
I use an ofFbo to generate some pngs.
When the app gets in the draw/update loop, it works as expected, drawing the first layer from bottom to top. But calling this in setup reverses the order and draws the first layer on top.
I could use an exception just for the setup phase, but there might be a simpler solution. I’am on the master branch.

    ofFbo fbo;
    fbo.allocate(x,y,GL_RGBA);

    fbo.begin();

    //clear with alpha
    ofClear(0, 0, 0, 0);

    //draw some stuff as first layer
    ofDrawRectangle();

    //draw some stuff as second layer
    ofDrawRectangle();

    fbo.end();

    //creating an ofImage to save it later
    ofPixels pix;
    pix.allocate(x,y,OF_PIXELS_RGBA);
    fbo.readToPixels(pix);        
    ofImage tempImg;
    tempImg.setFromPixels(pix);

Update: hm this works fine in a fresh empty project, so this must be related to the rest of my code. But still not sure whats causing this. See the screenshot below, #1is a png created during setup, #2 is created while runnnig, same function.

  fbo.begin();
    
    ofClear(0, 0, 0, 0);

        ofSetColor(0,255,0);
        ofDrawRectangle(0,0, 50,50);
        
        ofSetColor(255,0,0);
        ofDrawRectangle(0,0, 20,20);

    fbo.end();