CSS declaration "vertical-align: sub" is incorrectly rendered in Internet Explorer 6 and Internet Explorer 7

Actual results (live results in your browser):

vertical-align: sub

Expected results (screen shot):

Reference:
"sub
    Lower the baseline of the box to the proper position for subscripts of the parent's box"
CSS 2.1, section 10.8.1, vertical-align property

This testcase is rendered as expected with NS 6.1, NS 6.2, NS 7.0, NS 7.1, NS 7.2, Firefox 2.0.0.3, Seamonkey 1.x, Epiphany 2.14, Safari 2.0.4, Opera 9.20 and Konqueror 3.5.5

HTML 4.01 Strict compliant Valid CSS!