Display issues in different browser versions

Noticed an odd behaviour after moving to IE 8 from 7

The problem relates to Footer Blocks. At first I thought the cause was the content, but after reducing the content to a minimum the problem still appears.

Test method
Create three blocks nice and simple

Block 1 body content "1"
Block 2 body content "2"
Block 3 body content "3"

Insert Block 1 in Footer Block 1 , Block 2 in Footer Block 2, Block 3 in Footer Block 3

In IE 7 the blocks appear side by side
In IE 8 the blocks appear side by side
In IE 8 Compatability mode Footer Block 3 appears under Footer Block 1, with more content it can appear under Footer Block 2

I have made no major changes to the CSS, can anyone confirm? Any suggestions?

Thanks
John