Phpstorm 9.0.2 bug reproduction: Namespaced functions not detected

functions.php

<?php

namespace Foo;

/**
 * @return \DateTime
 */
function getDateTime() {
  return new \DateTime();
}

test.php

<?php

include __DIR__ . '/functions.php';

echo \Foo\getDateTime()->format('U'); // Warning: Method 'format' not found in class

# When I place the function in the root namespace, the function got recognised
# and I can autocomplete chain on its return value without a problem.
# But when the function is namespaced, PhpStorm 9 will not detect it anymore
# and it will throw an inspection error.
# (I'm sure this worked in PhpStorm 8)

https://youtrack.jetbrains.com/issue/WI-28993