Answer: Sounds a bit odd, doesn't it? Coleus is generally considered an annual, but keeping it indoors will extend its life. Usually the older leaves turn yellow and fall off, to be replaced with newer, more colorful leaves. If you keep the growing tips of your plant pinched back, you'll encourage bushy growth and force leaves to develop from the old leaf scars on the lower portion of the stem.
I suspect the older lower leaves dropped off your plant and were replaced with newer, brighter leaves, but the leaves midway along the stem are only now beginning to drop off. As long as the new growth looks healthy, don't be too concerned about the yellowing older leaves. Once they drop off new leaves will take their places.
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