How to reproduce : 

1- Create an exhaustive content (named Exhaus1 in this test), just fill its title. 

2- Create another exhaustive contente (named Exhaus2 in this test).

In repeater3levels field, fill :

• the string field
• the "belongs to" field with selecting"Exhaus1". 

3- Open Solr search tool and configure a research as follow : 

4 - In the result table, there is a line for Exhaus1 and a line for Exhaus2 : 

5 - Edit the repeater3levels of Exhaus2 and set a new value to the string value :

6 - Click on OK => Frame is closed. 

7- Following message is displayed, click on "Save". 

8 - Click on this message is order to update table :

9- A line has been added in "Exhaus1" => KO

Precision : when String of level1 of repeater3level is updated through content edition, no line is added.