Not possible to nest multiple progressbars

[StHagel]

Hey,
I tried nesting multiple progressbars like in this example:

#include <iostream>
#include "progressbar.hpp"

int main()
{
    ProgressBar pb1(100, 70);
    for (int i = 0; i < 100; ++i) {
        pb1.display();
        ++pb1;
        // Do additional stuff
        ProgressBar pb2(100, 70);
        for (int j = 0; j < 100; ++j) {
            pb2.display();
            ++pb2;
            // Do additional stuff
        }
        pb2.done();
    }
    pb1.done();
    return 0;
}

Unfortunately, this does not work. Instead the first progressbar disappears as soon as the second one gets displayed for the first time. After the second bar is finished, the first bar appears only for a brief moment, updates once, and disappears again.
Is there a way to nest two progressbars using the current implementation?
PS: If you want to run the example code, I recommend putting some sleep()/uslepp() in there, otherwise it will run too fast to notice.