In the example
(the same happens in 3.4.1)

The fieldset "Phone Number" has an height of 117px in Chrome 21.
In IE8 under XP, the same fieldset is 141px height.

I measured the same <fieldset> element, which contains:
- a <legend> (it is 2px higher in IE)
- a <div>, which is the same in both browsers

Forgetting the two pixels in the <legend>, it is something related to the <fieldset>.
Anyone noticed this?

I haven't tested any other version than IE8.