My guess is they let the roots dry out at the nursery, and it's finally showing the results now. I've had this happen with conifers. You could keep it and see if it recovers, but you've lost a lot of the plant's value in any case.

Shoot! I just dug it up and the roots look OK. any other possibilities?

Umm. Can you post a picture of the roots?

Or is your sheet compost bed still "cooking?"