A column break doesn't reset a child's bottom margin as per the note in http://www.w3.org/TR/css3-multicol/#column5 . Tested on 525.13 (nightly rev 31076).
This might be related to Bug 14881.
Firefox 3 B4 renders this correctly.
Testcase to follow.
Created attachment 19813 [details]
Testcase for column break not resetting child bottom margin
Sorry, totally unrelated to Bug 14881 (that bug has nothing to do with CSS columns).
I think this is happening because children of div are getting treated as block element, due to this it will try to fit those in the same column and when it is not getting fit in the column then it will get break to 2 blocks and it will get displayed in the next column..
But in FF it is treated as the inline flow, As I have tried to remove last 2
<div></div> then I am getting 7 blocks in the FF, But the webkit behavior is quite consistent.
So I thing above is the reason for this issue..and current webkit behavior is the normal expected behavior, as I have tried in IE also their also the children of container div are getting treated as block only..