OK... the layoutproblem has to be solved in .php/.js (any volunteers?)
If setOpenTab() is not set, every open tab has class="toggle" and every closed tab has class="toggle closed"
If setOpenTab() is set, things change to the unexpected:
Open tab (default open by setOpenTab()) has class="toggle closed"
Closed tab (normal) has class="toggle closed"
Open tab (normal) has class="toggle"
And after closing the tab that's open by default:
Closed tab (default open by setOpenTab()) has class="toggle"
Closed tab (normal) has class="toggle closed"
Open tab (normal) has class="toggle"
The tabs that aren't involved in setOpenTab() aren't affected.
I was working on a CSS-workaround, but just discovered it also affects the toggleOpen/toggleClosed images (I overlooked that before). So here is a CSS-file for everyone who really really wants to use the setOpenTab()-function. It's even without those images, so it's not as nice as the other one (imo), but it's still nice enough.