I’ve found it last night while trying to update my status in twitter. these days I am too much twittering and I was redirected to an url while exploring twitter. while trying to update my status, it failed repeatedly and then i’ve found that bug – lol
the url that reproduces the bug is http://explore.twitter.com/home – which looks similar to your actual twitter home (http://twitter.com/home) and it also shows you a twit box to update your status. but you cannot update your status from http://explore.twitter.com/home
check what was returned after the ajax request (u have firebug, right? do it yourself)
403 Forbidden: The server understood the request, but is refusing to fulfill it. If you are posting from an API tool please ensure that the HTTP_REFERER header is not set.
try before they fix it 🙂 interesting usability bug indeed.