Windows keys can't be detected

I have a very simple script at the start of Update function:

if (Input.GetKeyDown(KeyCode.LeftWindows) || Input.GetKeyDown(KeyCode.RightWindows))
{
  print("Windows key is pressed");
  return;
}

But it doesn’t work. The rest of the Update codes run perfectly, though.

Unity 5.4.2f1, Windows 10.

Is this Windows Standalone or UWP?

Both.

Yikes, please report a bug. Sounds like you have a nice small repro project.