[ofxCv] RunningBackground - getForeground doesn't get what I expected

Hi everyone, I am using RunningBackground to get foreground countours

ofApp.h

ofxCv::RunningBackground background
ofImage thresholded;
ofImage grabFg;
ofxCvColorImage			colorImg;

I wanted to get the foreground countours by running the average background method of the RunningBackground class, however I get the image from the webcam/kinect as it comes without processing and not the foreground.

ofApp.cpp

        background.update(colorImgSmall, thresholded);
        cv::Mat fgImg = background.getForeground();
        ofxCv::toOf(fgImg,grabFg;


Instead I have to do the following:

       background.update(colorImgSmall, thresholded);
        thresholded.update();
        img.setFromPixels(thresholded.getPixelsRef());
        img.erode();
        img.erode();
        img.erode();
        img.blurGaussian(27); //27 29
        img.dilate();
        img.dilate();
        .....

OF 0.8.4
Ubuntu 12:04 64 bits.

Thanks in advance, best!