Steps to reproduce

1. Install Ibexa
2. Go to Admin -> Roles -> Assign to User/Groups on Anonymous role
3. Click 'Select User Groups'
4. Select 'Guest accounts' group
5. Confirm selection in UDW
6. Save and close new role assignment
7. After reload you will get notification with error that 1 is already assigned
8. Click 'Select User Groups' again

Result
UDW opens and immediately closes, JavaScript error is thrown.

Expected result
UDW opens normally.

 Note
The same issue occurs not only for user groups but also for selecting Users