nana place bug

#pragma warning(disable: 4996)
#include <nana/gui/wvl.hpp>
#include <nana/gui/widgets/button.hpp>
#include <nana/gui/widgets/label.hpp>
#include <nana/gui/widgets/textbox.hpp>
#include <nana/gui/widgets/panel.hpp>
#include <nana/gui/detail/basic_window.hpp>
#include <nana/gui/place.hpp>
using namespace nana::gui;

#include <sstream>
#include <iostream>
#include <functional>
#include <unordered_map>
#include <sstream>
#include <numeric>
#include <memory>
using namespace std;
using namespace std::placeholders;



int main() {

    form fm(API::make_center(400, 300));
    panel<true> left(fm);
    panel<true> right(fm);

    place plc(fm);
    plc.div("<<weight=100 left><right>>");
    plc.field("left") << left;
    plc.field("right") << right;
    plc.collocate();

    // left area
    button btn(left);
    btn.caption(L"btn");
    place plc1(left);
    plc1.div("<btn>");
    // plc1.field("btn") << btn;
    plc1.collocate();

    // right area
    button top(right);
    top.caption(L"top");
    button bottom(right);
    bottom.caption(L"bottom");

    place plc2(right);
    plc2.div("< vertical < top> < bottom weight=30%>>"); // it's ok for 30, but not for 30%

    plc2.field("top") << top;
    plc2.field("bottom") << bottom;
    plc2.collocate();


    fm.show();
    exec();
}