Ok, that fixed it.

Seriously: re-enable icon customization, switch to Desktop 1, disable it.

What's curious is that when I look in "c:\Users\<me>\Desktop" I see what appears to be all of the icons I appear to be missing. I also looked at the few icons that ARE displaying on my desktop, which are placed approximately where I placed them, and NONE of them are listed in that folder. However, I also noticed that "c:\Users\Public\Public Desktop" does have all the icons that are currently displaying. I'm confused.

Re-enable icon customization, switch to Desktop 1, disable it.

Sigh. I've reverted that, but it looks like most of my desktop icons are gone. This is odd, because I use a tool for saving my icons placement, and "Restore"ing that doesn't do anything.

Settings > Switching Desktops > Customize desktop icons.

I don't know what I did, but I think there was some dialog that was presented to me with something about a choice for "icons", and now I have a different layout of icons on each desktop. What is that option? I want it back the way it was.