Snagged while starting to learn custom GUI programming

I've been taking the first steps toward making a custom interface for a very custom machine. I found John's great introductory step-by-step tutorials and have started following along and running them. I got to a point where I think I've followed all the instructions but the behaviour I'm seeing isn't right and doesn't match the tutorial Accordingly, I was hoping someone here would be so kind as to point out why the inconsistency.

The tutorial link is here: gnipsel.com/linuxcnc/gui/gui01a.html

The trouble starts around step 8-10, where we're adding an action and a toolbar button. I did both and ran the program, but in neither the development environment or while running the program do I see the correct icon (red circle with "X"). Instead, the button is shown with the label, as below. It works as it should, enabling and disabling the e-stop like in the tutorial but without any graphics.





For completeness, though I doubt it's related, I'm running this in Oracle VirtualBox. LinuxCNC gives me some realtime errors when I run some configs, but I don't think this is a problem for what I'm trying to do right now.

Your tips and solutions are appreciated.

I missed a small detail when I was going through step 8, which was to set an icon for the action. For some reason I was thinking that there would be a default icon because each action had it's own shown in the palette on the left.

Everything works as expected now.