I guess this is a theme issue, as I don't remember there being a problem with the old moodle.org theme.

Reassigning to Martin for consideration.

html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, font, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td {
margin: 0;
padding: 0;
border: 0;
outline: 0;
font-weight: inherit;
font-style: inherit;
font-size: 100%;
font-family: inherit;
background-image: none;
}
/* IEs break with vertical-align: baseline on images */
/* set different vertiacal-align for tr, th, td for Moodle */
html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, font, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead {
vertical-align: baseline;
}

should not be used for sub and sup. The former code sets font size to 100% and the latter sets vertical-align to baseline which breaks supscript and superscript...

Anyway, I took our sub and sup as they are hardly the sort of tag anyone uses for anything else.

Cheers!