User not created when registration information isn't correct when creating new user in new Administration UI

• XE 1.9 SNAPSHOT 17115
• Go to .../xwiki/bin/admin/XWiki/XWikiPreferences?editor=globaladmin&section=Users
• Click on "Add new user"
  • Enter First name, last name, user name
  • Enter 2 different passwords ("plop" in the first field and "hulk" in the second)
  • Click on "Save"
  • The dialog box closes, no new user is created
• Click on "Add new user" again
  • Do not enter a login ID
  • Enter first name, last name, email
  • Click on "Save"
  • The dialog box closes, no user is created

Basically, whenever the information provided in the user creation form is not valid, the page reacts by doing nothing instead of providing the user with feedback about what he didn't do right.

Instead, the page should display an alert or a message asking the user to correct the information (as it's done on xwiki/bin/register/XWiki/XWikiRegister when the information provided isn't correct).