AEM Useradmin: Adding member to users impersonators list doen'st retain the previous members in the list

AEM Useradmin: Select userA profile which is having userB,userC in its impersonators tab.
Add member userD to userA's impersonators list and save.
When we refresh, userA doenst retains the previous members in the impersonatorsList.

But its just the newly added member userD in the userA's imersonators tab list.

We see a post call, in browsers network tab with
url localhost:4502/home/users/A/id
data: memberAcion = sudoers
          memberEntry = userD

Do we know the file? which triggers this post, so that we can ensure the post retains the previous members if so any in its memberEntry.