[css3-break] How should this break? (breaks in the margin area)

Hello Elika, Rossen & everybody,

I have a question regarding an edge-case for unforced breaks that doesn't seem to be specified anywhere.
What happens when an unforced break occurs in the middle of the margin of the last child of a block container that has a border? You can see this scenario in [1], with multi-col. Should the part of the margin *after* the break be discarded (Gecko[2]) or should it be preserved (WebKit[3], Opera[4])?
And more importantly, what part of this spec (if any) describes this case?

Thanks in advance,
Mihai

[1] https://dl.dropbox.com/s/f5yn1dsd5tau9nu/break-big-margin-in-columns.html
[2] https://dl.dropbox.com/s/5hjm3cfnqw4djoi/firefox.png
[3] https://dl.dropbox.com/s/xuddm1zbsnof6o5/Chrome.png
[4] https://dl.dropbox.com/s/a0jusfj4zdqadxz/Opera.png