meelosh - 6:16 pm on Jan 11, 2011 (gmt 0)

@andyA i have run into similar issues in the past if you are dealing with "exact" spacing meaning there is no padding overflow all content in the containers fit exactly to the last pixel....especially if you are floating content in list format..different browsers have different pre sets on padding and margins...so if it is not zero-ed at the beginning and there is no room for fluctuation then the floats bump each other or other containers and all hell breaks loose.
I dont know if this is your problem (sounded similar)but bottom line is i always leave a little room for fluctuation so this does not happen and make sure i *{padding:0;margin:0;}....hope this helps?