Hi.

Adding new items in a collection bloc removes the previous ones.

Steps to reproduce:

Install a clean version of eZ Platform 3

Create for instance 4 articles.

Edit the home page and add a collection bloc. 

Select 3 articles and add them to the collection bloc, and save and publish.

Edit an other time the home page, edit the collection bloc which already has 3 articless, browse and add an other article.

=> The 3 previous articles have been removed

This behavior only affects version 3 of Platform.