Ubuntu – Laptop suspends on shutdown with lid closed

I'm struggling to phrase this question very coherently, but here's what I'm struggling with…

I have a Lenovo laptop from a few years ago. Recently, I put ubuntu on it. As it stands right now, I've connected it to my ol' setup of monitor, keyboard and mouse, so the laptop itself sits in a corner of the desk, lid closed.

So my setup is like this: I've got my corsair k70 under my hands, my steelseries rival mouse on the right, the dell u2713hm up front… and the laptop sits underneath the monitor, lid closed with everything hooked to it.

The problem: When on my main monitor, the u2713hm, if I issue a shutdown the system will instead detect the laptop's lid is closed and interrupt the shutdown to suspend the laptop instead.

How to fix? This issue was similar, but its proposed solution did not have any obvious reaction.