Just letting everyone know -
I was moving my keyboard around tonight, and I later tried the Media button, and it's working correctly now.
Not sure what happened, or what changed, but at least it's working.
I'm just worried that there really is some issue there, which is no longer able to be diagnosed, that will come up again later, once the warranty is up...
I guess there's no point in bringing it in for repair now, though I'd love to get whatever caused the issue replaced, just in case...