Moving from the S4 to the S7, I was glad to see this feature still included. But I've noticed that unlike on the S4, it doesn't seem to require a flat surface anymore. I've held my S7 up vertically and I could still wave my hand and unlock it. This makes me worry that it might come on at pretty much any time if it detects some movement. Is this normal? Even the description mentions a "stable" surface, but it doesn't seem necessary.