Overflow auto fixed my problem but why?

On this page http://tutorial.davidclick.com/philpotts-clone.html & illustrated here http://i216.photobucket.com/albums/cc53/zymurgy_bucket/overflow-auto-mystery_zps1b64d973.jpg I added a overflow: auto; to the #header & that preserved the height of the conatining div.

But why did this work? The reason I ask is that i understand overflow: auto; is a fix to the known problem “If floated elements habe non floated parent elements, the parent will collapse.”

So my question is please…

“Why did overflow:auto; preserve the header hight & prevented it from collapsing”

Grazie tanto,

What version of Firefox are you using as I could replicate it in Firefox 18 or Chrome 25

Likewise, I don’t see overflow:auto doing much there. What do you mean by “collapsing” in this case. Not much changes with overflow: auto turned off … not in my browser, anyhow.

Grand aplogies the overflow:auto it is totally redundant, apologies for the red herring but it does figure that is should have no effect.