Layout seems fine in designer, but floating divs don't work on front end. CSS problem?

Dear community,

I am trying to create a custom layout for a group profile. In the layout designer I created a row including two regions next to each other, one for content, and another, a sidebar on the right. Looks fine in the designer. I fill it up with content, but in practice the sidebar is situated under and not on the right of the content region. If I change the order of the contents in the sidebar, they change order on the front end as well, so I suppose the layout designer does something, but not placing the regions correctly.
Looking into the HTML source I see the relevant CSS values in the divs, but tracking them with FireBug I don't find any css files (or css generator php) concerning their positioning.
Am I doing something wrong, or is it an bug? How can I make a working sidebar with the Layout Manager?
I am new to panels and pages, please excuse me if my problem is irrelevant or too simple (or if I am posting it in the right place, or should place it under Chaos Tools or Organic Groups). Thank you for the help and inputs!

Organic Groups is version 7.x-1.1
Drupal is version 7.8
Chaos Tool Suite is version 7.x-1.0-rc1