If a Square Grid update does not seem to be working

Before you do anything else, go to your Theme Settings and try toggling on or off the Responsive Design support (choose the opposite of what you want) and saving, with the Registry Rebuild checkbox selected. Then refresh your test page. Then change the Theme Settings back to how you want them, still with Registry Rebuild selected. The relevant stylesheets should be loading properly now. It seems that there are instances where Registry Rebuild alone does not force re-reading of the theme configurations.

I am looking into adding some default settings so that this process is not necessary. (I'm assuming this is not a theme engine bug.)

Meanwhile, this reconfiguration process should do the trick. My apologies for the headaches this may have caused.