In Firebug you can see that the main-content div is inside the leftcolumn on the events page cited below. This makes the page impossible to edit... but somehow ok on preview. It makes me wonder if maybe there is some missing closing div in the edit mode somewhere that would collapse these to together.
https://www.jboss.org/author/events/JUDCon/2011/boston.html?mgnlCK=1317138815365&mgnlIntercept=PREVIEW&mgnlPreview=false

(see screenshot of how it is, and how it should be)

Cheers,
Cheyenne