Can't add user to group after its creation

build: nuxeo-server-9.10-I20171115_0206-tomcat
Browser: Chrome on MacOS

Steps to reproduce:

• Go to User & Group
• Create a jdoe user without any group
• Save
• Go to his profile, add him to the member group
  => 404 is displayed
• Go back to his profile
  => the sentence "jdoe is now member of " is displayed even if a 404 was displayed
• Click on Remove
  => "Do you really want to remove jdoe from undefined?" is diplayed on a popup
• Click Yes
  => a 404 is displayed