This is an odd one (for me atleast), I decided to investigate this further. First I must say that, that page has some pretty bad validation problems including a missing end div and some oddly placed li elements among others.
But this wasn't the problem it is actually quite simply it seems that the border attribute and font-style don't play well together in IE. Removing one of the two fixes the problem.
I tried searching for this bug but I didn't find anything similar but there are a few bugs that include the border attribute with the blockqoute element so perhaps this is a variation. Or maybe it is something else.
Hope this helps.