User picker doesn't allow to select back a user once removed unless losing focus

Reproduction steps:

• Create a user Foo
• Go to the XWikiAdmin group and edit it to add users (or access any user picker: this step is only about obtaining a user picker)
• In the user picker type "Fo" and select user "Foo" that should have appeared
• Use backspace to remove Foo
• Without losing the focus in the field, type again "Fo"

Expected result:

• the user "Foo" should be proposed again to be selected

Obtained result:

• the user "Foo" is not proposed anymore to be selected

Note that if the focus is lost (e.g. by clicking outside the input field) after removing the user from the picker, then it's possible to select again the user afterwards.