Actual results (live results in your browser):

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