I have JetPack 2.9.3 installed. I am connected to Twitter, Google+ and Tumblr.
Yesterday, (4/28/14) I had two posts to my WP site and both were set to post to all three of the above as well. They were scheduled at 1pm and 3pm respectively. The first one posted to WP but not to the sites I am connected to. The second one posted to WP and all of the sites I am connected to.
Today (4/29/14), I had one post scheduled, which posted to WP at 1pm but did not post to any of the sites I am connected to.
As far as I can tell, there was no difference in the setup for these posts. All check boxes were checked. I did update the custom message on all three of them as well.
I have one post scheduled for 4/30/14) that is also set to update the 3 sites. It also has an updated custom message on it. I will see how that goes and update this post following that event tomorrow.