Steps to reproduce:
1. Create a landing page
2. Add a schedule block,
3. Add first content to the schedule block,
4. Move the slider on the timeline to next hour,
5. Add another content to the schedule block,
6. Repeat steps from 4 and 5 and 4 again,
7. Add a content that were added in 5 step.
8. Notice that timeline displays 4 changes in schedule block,
9. Publish landing page,
10. The timeline displays 4 changes.
11. Go to the landing page edit where you edit just published landing page,
12. Notice that there are only 3 changes visible on the timeline.

Expected result: There should be displayed 4 changes on the timeline.

It looks like the content that was added twice to the schedule block disappeared. Only the last change with given content is saved.