tt's, font-family inheriting and font-size: a bug

The css in the head of this file is like this:

html, body {
    font-family: Verdana;
}
tt, span {
    font-size: 0.8em;
}

The two columns below show that inheriting the font does not correctly inherit the font-size for a <tt> block.
<tt> <span>
font-family: Verdana; font-size: 0.8em; font-family: Verdana; font-size: 0.8em;
font-family: inherit (Verdana); font-size: 0.8em; font-family: inherit; font-size: 0.8em;
font-family: Verdana; font-size: 1.0em; font-family: Verdana; font-size: 1.0em;
default font; font-size: 0.8em; font-family: courier; font-size: 0.8em;