The collapse in the theme header uses the smc_Toggle JS object. That function takes only a list of elements to show/hide, and as far as I can see it can't hide one and at the same time show another. Looking at your images, you're not just swapping elements as it usually does, but actually reordering the layout. This is a problem since the toggle function in SMF can't handle that. You'll likely have to write your own function to swap it, maybe using JQuery to save time. Do you have any experience writing JavaScript?