I've got an Asus GL552VW running Ubuntu Gnome 17.04. With a monitor connected to the HDMI port. The monitor is the primary screen and the laptop screen the secondary.
When i boot to the login screen with the lid closed i get the login screen on the laptop screen (even though i can tell by peaking the screen isn't even on) and nothing but the blank grey background on the monitor. If i open and close the lid then the login screen switches to the monitor.
I tried setting the screens to being mirrored to show the same thing on both screens. But after rebooting (with the lid closed) it still behaves the same way.
I got dual boot with Windows. And there it isn't an issue. So i doubt it's a hardware issue.