IE has typically had issues with displaying CSS per the Standard so there is code that is designed to check your browser and if IE .x is found apply a specific fix to view it correctly.
I've not reviewed the code in detail though myself so I can not point out the exact fixes implemented.
Community MX a site for Adobe products used for Web Development though has some good articles on how to fix code for all browsers and they show like 15 different browsers and all appear to look the same when used with their coding.
