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I might also suggest a couple other things...one possibility is sunburn/windburn...and the other is possibly Pythium splendens, a fungal infection...it will cause leaf tips to yellow and eventually rot the plants roots. There is also Phytophthora palmivora, the common root rot fungus, but it starts at the base of the plant rather than the tips and would be very obvious.
Thanks everybody, too bad because I found the yellow-tipped appearance really striking. But this explains why I couldn't find any cultivar that looks like it. Kind of weird though that a liriope would be diseased or damaged by weather, they are so tough. And that the disease would be so uniform. I'll have to take another look at it now that it's cold. If I get to do that I'll take a pic & put it up here.