This sentence should be rendered with a font-size of 32px (expected results) and not a font-size of 8px (actual results).
Tahoma is the default font face for message-box on Windows system; the default font-size for message-box on Windows system is 8px.
"System fonts may only be set as a whole; that is, the font family, size, weight, style, etc. are all set at the same time. These [font subproperty] values may then be altered individually if desired."
coming from CSS 2.1, section 15.8 Shorthand font property: the 'font' property
Firefox 2, Firefox 3.0.1, Shiretoko 3.1, Opera 9.52, Safari 3.1.2, Konqueror 3.5.9, Amaya 11 build 20081216, Seamonkey 1.x, Seamonkey 2.x, NS 7.2, K-meleon 1.x, Galeon 2.0.4, Epiphany 2.22.3 all pass this test.
This bug has been reported at connect's IE beta feedback as bug 361181.