How to reproduce : 

Point number 1 : 

1/ Create a project with an illustration (among already present illustrations) and click on validate. 

2/ When project is created, click on   button and click on "Update project" menu. 

3/ Page to update project is opened, but project illustration is present twice (3 times in my case since I click 2 times on "Update project"). 

Each time project is updated, an illustration is added. 

Point number 2 : 

1/ I update a project illustration with an image in the right of carrousel.  I save the update. 

2/ I edit the project : selected illustration is not first, it stays at the right of carrousel : 

(If I understand correctly, selected illustration should be first)

Point number 3 : 

I do not know how, but I have a project with following illustration : 

In this particular case, I cannot edit and click on Validate on the project : it stays on edition page (I haven't seen any error message). 

 

Point number 4 : 

During different tests of illustration, I have several projects (from project1 to project5). 

I update illustration of project5, and illustration of project1 has also been updated. 

I do not manage to reproduce this behaviour. 

Point number 5 : 

(This point is maybe linked to points 4 and 5)

To reproduce : 

1 - Create a project and select an illustration (among proposed illustrations)

2 - Update this project, and change the illustration, by selecting an image on your computer. (by clicking here : 

3 - Click on Validate button => Project illustration is updated with locale image. 

4 - Update the project, and change the illustration, by selecting an illustration among proposed illustrations. 

5 - Click on Validate button => Project illustration has not been updated.