I've only seen the "phantom segment" on DL.com, never on the app. And, the appearance of the "phantom segment" is but one of the apparently dozen obscure steps required for successful application of an RUC to a reservation. I've had a "phantom segment" yet at T-24 check-in, was well down the upgrade list. Checkin is the ONLY way to know for sure an RUC was applied correctly, and of course by T-24 it is too late to tell if you would have cleared days earlier had every one of the dozen obscure and easily mis-typed steps been done correctly.