We have a shared photo stream that my wife and I add photos to and we share them with the rest of the family. When either my wife or I add photos to the stream, they do not show up on all devices. In fact, if one does not show up and I test with another photo, the later one shows up, but the original does not.
The stream is set up to allow subscribers to add photos and we are both using iOS 7 on iPhone 5.
You can apparently force ios6 devices to receive the subscriber contributed photos by turning off shared photo streaming and turning it back on again. It is under General Troubleshooting in the following link:
A similar workaround did not work with iPhoto 11.
To get around this, I've been re-sharing the subscriber contributed content and deleting the original from the stream. They show up, but not a very elegant solution.