Problem picking seat
 

I am looking at a ticket IAD-JNB and on return CPT-IAD. I was thinking about buying business on the way to JNB and economy on the return. The business is a special fare so I know I cant pick seat but the economy is a flex. I should be able to pick my seat for the economy flex but it wouldnt allow it when I priced it out. If I pick economy seats round trip it will allow me to pick up my seats.

Is this a glitch or could I pick seat after I purchase the ticket?

That appears like an IT glitch to me. The booking engine sees the J Special fare and applies the 'no seat selection' rule to the entire ticket. A family member of mine booked Y Saver out and Y Fles in and could certainly select a seat after booking. She did not try to select her inbound seat at the time of booking, so I can't say if she encountered the same IT glitch as you seem to have done.

Only in Y can you choose seat at time of booking (if eligible) so the J segment is probably throwing things out.

I have similar ticket (J saver) and Y saver but have been able to book seats on my J leg of journey

Before paying and receiving your booking confirmation?

You should be able to do it after ticketing either way and if not you can always use the online chat or call for a quick allocation

no, after I had paid.