In other words:
"User:newFromId should not set ItemLoaded['id'] = true"
$ php maintenance/eval.php:
< $u = User:newFromId( 1000000000000000000 ); // Exa-, 10^18
< $u->getId();
1000000000000000000;var_dump( $u->isLoggedIn() );
true
$u->isItemLoaded( 'id' );
true
Bumped into this while fixing T42340 (bug 40340).