IE7 jQuery Accordion: when I click on header, content is not visible until hover over it..

Question

I had to create a jQuery-accordion for a form. It works as it should on FF3, Chrome and Safari, even on IE8. But when I view it in IE7 there is this weird bug: I click on the accordion-header and the accordion opens, but the content is not visible. When I hover over it though, it shows up. It has no validation errors nor javascript errors. Could you figure out what's the problem in this case?

Here is the link to the page: http://www.aussenwelten.ch/cms/index.php?option=com_content&view=article&id=43

Thank you in advance!

EDIT: I have set the IE8-view-mode to IE7, so everyone with an IE8 can see it too.