Now, this takes me back. When I started writing about technology this stuff was commonplace. A software company would announce a new version or a new package, its target date would come and go and then it would be released as buggy as anything. Windows itself didn't get it right until version 3.1 (3.0 caught the imagination of the market, 3.1 worked a load better).
The fact that this doesn't happen any more is to be applauded = except here we are with Twitter issuing a new tweak and unissuing it within days. We'll gloss over the fact that you could already retweet manually.
Half of me hopes this isn't going to mark a return to the bad old days - for 'software company' read 'social media company' but the idea of premature releases remains constant. The other half of me is rubbing its hands saying 'here we go again, software people back on form...'
One possible explanation can be that the decision makers pushed for that certain day and then the developers created something but it was not in "perfect" shape. Its like being pushed for last minute report.
Like you said, you can retweet manually. The only people who are affected are the power retweeters I would assume. As Twitter is a free service, I doubt people will get as outraged with this than if it was a product from Microsoft.