The same itinerary cancellation occurs if someone uses a cheaper "hidden city" ticket (i.e., JAX->ATL->LON), skips the JAX->ATL segment and just shows up at ATL to take the transatlantic flight. Once the passenger misses the first segment, the remaining flight itinerary is cancelled by the airline. This has been discussed often in the forum and here's a recent thread, citing another.

[As Moderator, I edited the OP's thread title to more precisely describe the topic. Ocn Vw 1K.]