Ubuntu won't shutdown when connected to an external screen

[Slapino]

Hi all,
I'm running Ubuntu 17.10 on an Asus n56vz laptop.
A couple of years ago I took the optical drive out and replaced it with a 128gb SSD, so i would have two HDD'S. (I have no idea if that's relevant).
I have dual-boot, Ubuntu 17.10 (which i recently upgraded to from Ubuntu 16.04), alongside Windows 10.
The problem is whenever the laptop is connected to an external screen (which is all the time basically), Ubuntu won't shutdown. Instead, i'm just getting a black screen with a blinking cursor and the only way to shutdown is to hard-shutdown it using a long press on the physical button.
Once I disconnect the HDMI port, Ubuntu shuts down normally.
I've read countless threads, some had some relation to my problem (most of them relate UEFI), but I couldn't get anything to work (may be because I'm a noob).

Any guesses?

Thanks!

EDIT : Ubuntu will shutdown using the [sudo shutdown -h now] command, but i don't know how this command works, if it's forced, can it cause file corruption ? is it ok to poweroff everytime with it?