The site wouldn't let me type in the details field, so I'm typing details here.

It's been indoors a couple feet from a partially obstructed south window in Eugene, OR, so not much chance it got sunburned. I moved it to the larger pot you see a couple weeks ago when I first saw these strange spot and yellowing, and I'd mostly ruled out over-watering as the culprit, but it continues to happen, and it was only moderately pot-bound in its 8-inch pot anyway.

I've checked it over for any kind of critter and I've found no sign of anything: no specks or webs or honeydew, etc. I sprayed it with some 3-in-1 for good measure because it's one of my favorite plants and I don't want to lose it, but the spots keep right on happening.

It seems the lower/older leaves are affected the worst, but as you can see, some fairly young leaves also have spots. The spots appear first, and then the affected leaf yellows and dies.