Just search for any of the emails. On the search results page, select a few mails by checking against their checkbox. Now hit the ‘Spam’ button. What you see as a result is an empty blank page. You have no option but to either type another URL in the address bar or hit the browser’s back button. If you go back to Inbox, the mails will still be there and would not have been marked as spam/ moved to the spam folder.
Not having the spam button work at such a prominent place is bad design. Yahoo please fix it!!!