user can't be added to group

issue is reproduced in standalone mode
branch feature/rbac-roles

Steps to Reproduce

1- Create a user with no groups

2- Create an empty group

3- Go to group created in previous step and go to Users tab

4- Press Add

5- Look for user created in step 1

6- Click Add

Actual Behavior

Actual result: Add button does nothing

It's always reproducible

Note: users created via API are added correctly to the group

Expected Behavior

Expected result: User is added to the group