All copies of a content items are added to project items when DnD via content referent list

Description

Steps to reproduce

1. Enable project mode.
2. Assume that the project selector is choosing a project.
3. Create a block named Blk 1.
4. Drag and drop Blk 1 to a content reference list of a page four times.
5. Notice that there are 4 copies of Blk1 in the content reference list property. This is OK.
6. Select all copies of Blk 1.
7. Drag and drop the copies to project items in step 1.
8. Observe the project items.

Expected:
Blk 1 is added to the project items.

Actual:
All copies of Blk 1 are added to the project items, project overview of current project.

If a user changes the status of one copy, the other copies disappear.