It looks like they announced they will be making a concession to bring back at least some of the old behavior: http://blog.twitter.com/2009/05/we-learned-lot.h

It looks like they announced they will be making a concession to bring back at least some of the old behavior: http://blog.twitter.com/2009/05/we-learned-lot.html http://blog.twitter.com/2009/05/we-learned-lot.html The jist: they're bringing back the old behavior only when the message starts with @username (and hasn't been created clicking the reply icon). It sounds like they made a technical change which trumps the actual message content with a piece of reply-to metadata, which is either explicitly included by the client or parsed by their infrastructure. Previously I believe it was "dumb" and didn't examine anything, and it was up to the client to filter based on the content of the message when it came to showing half-conversations.