Need Help with the BeautifulSoup problem, please

[seaspeak at gmail.com]

    I need to replace all tag <b> with <span> after ■. But the result from below is '■   <span style="REPLACE">D</span> / <font></font>'
Can you explain what I did wrong, please.

    s = '■<b>A</b> <b>B</b> <b>C</b> <b>D</b> / <font></font>'
    soup = BeautifulSoup(s)
    for i in soup.find_all(text='■'):
        tag = soup.new_tag('span')
        tag['style'] = 'REPLACE'
        for ii in i.find_next_siblings():
            if ii.name=='font' or str(ii).lstrip('')[0:1]=='/':
                break
            else:
                if ii.name=='b':
                    tag.string=ii.string
                    print(ii.replace_with(tag))
    print(soup)