Bug or not with overflow:hidden ?

[Shift]

Hi all,

I found a strange change in the display of my website with Konqueror 3.2 and 
Mozilla 1.6 / Firefox 0.8. A bug space was added betwenn the column of my 
site.

I found the responsable but regarding that 2 engines add change the way they 
react regarding my site I need your expert advice to told me if it is a bug 
or a feature. I vote for bug :-(

Here is the testcase : http://shift.freezope.org/css_lab/test/div
You can see that overflow:hidden + margin doesn't react has margin (alone)..
If it is a bug I will submit it to bugs.kde.org and bugzilla.mozilla.org 

Thanks, 

Franck