Originally Posted by alect
I think they won't let you check in on a one-way ticket unless you are a US Citizen or Perm Resident - USCIS restriction I would guess.
Yes, I've had this before. Returning to the US from the UK on the final segment of a seperately booked EWR-GLA-EWR on CO, checkin at GLA demanded to see a return booking so I had to go to the BA desk to print out a receipt for my JFK-LHR booked for a month later.