Akry & MarkL,
I tried holding down the button as suggested but it didn't work. Although I can certainly live without the "one-touch/express" function on this one window, my engineering instincts remain bothered by not knowing what is causing it.
Thanks anyhow, guys. I had an inkling that the symptoms were too odd for anyone to have seen before.- I'll call the dealer to see if they've seen this before.