What IE8 setting might cause small text to be rendered as normal-sized text (some “minimum font size to display” setting)?

Question

IE8 (on Windows 7) is not rendering the very smallest fonts on our website as small, but rather as normal size (100% of normal text size).

However, on a fresh install of Windows 7 (in virtual pc) with fresh IE8 installed, it renders properly.

I'm guessing there is some setting afoul. I've checked:

• Page> Zoom 100%
• Page> Text Size : Medium