Ok, have an odd thing going on, maybe someone can explain:

I am looking to fly me, wife and 6 year old to UK to visit my mum. We are pretty flexible from 20th June to 3rd July. Anyway, I have be doing the whole laborious searching for R available seats, but to speed things up, I just search one way EWR to LHR (as that is the only leg I care about and will upgrade) . Anyway I JUST found on 2nd July the 22.30 ewr to LHR landing 10.10 has R=6 which is perfect. However, when I then extend the search to be actually PBI to LHR , that exact same flight says R=0 !!!!! Does that mean I need to book a return ewr to LHR and a separate PBI to EWR return , just to get the R space on the EWR to LHR leg ???!!! Very odd. Any ideas ? thx