I think this is because you have a Background Begin in the left column and a Background End in the right column, and this is messing up how the columns display when you view the page.
Try keeping the begin/end in the same column and hopefully it'll work out! It'll never work propery with begin/end in different page slots.
That said - I'm not sure how effective using the Background Begin/End includelets will be with a multi-column layout, because the background image won't be restricted to just the column it's in.
I've only ever used the Background includelets with single column displays, a like these examples: Superhighways, Refugee Advocacy Forum, Women's Budget Group.
Thanks!
Joe