Persistent Live USB only remember settings on Laptops, not Desktops

Intention / Goal:
* Create a Trisquel 7 Live USB where I can install and run additional software, run updates and edit settings which are saved between reboots and on different hardware.

Problem: Whenever I ...
* boot the Live USB from laptop computer: Everything works fine, and my settings and software are present.
* boot the Live USB from desktop computer: No personal settings or software are present

What I've done:
Created a persistent Live USB with Trisquel 7 using usb-creator-gtk.
(Persistent means that the USB has been allocated extra storage space so that you can install software and change settings that will be saved between reboots. The bottom slider setting in usb-creator-gtk will enable persistence on your USB)

The Live USB was successfully created. Booted it on my laptop and ran $ sudo apt-get update && sudo apt-get upgrade. Installed some additional software and edited some settings. (Tip: NEVER run a dist-upgrade on a live usb. It will ruin all your hard work! Learned that the hard way.)

Rebooted to double check that all the changes had been saved, which they had. Tried it on two additional laptops to make sure. Booted it on a desktop computer at work to discover that nothing is there except a vanilla trisquel session.

What? How come?!

I've noticed that whenever I boot on a laptop, I am presented with the SYSLINUX 3.63 prompt with the cursor blinking at "boot: _". I write "live" and hit enter, which in turn boots the live session. On the desktop computers, however, I'm presented with the GRUB Boot Loader, where the only viable option is the Trisquel Live Session.

Maybe this difference has something to do with this issue?