Thank you for the information Toshimi. This is very odd as I've not been able to replicate the error.
It 'smells' to me that you have some content on the page that is breaking the mark-up and thus causing JavaScript to break. Please could you see if the issue happens in the 'Clean' theme too.
Is the site public on the web?
Are there any errors on the browser's console? (Press F12 and refresh the page).