"Display collection" deletes page contents without warning

[jiru]

I have been testing on https://app.sparktype.org/ and I found this usability issue.

Steps to reproduce:

1. Create a new page
2. Add some content
3. Toggle the right sidebar
4. In the right sidebar, toggle "Display collection" on
5. All the content added in 2. is now permanently lost, even after toggling off "Display collection"

Expected behavior:

5. The original page content should be back after toggling off "Display collection", or at least some confirmation about permanently loosing page content should appear.