Weird - I have booked 8 rooms onsite with Orbitz since 2/1/2016 (we're doing 2 split stays, and I change my mind alot!) and every time the 6 'digit' confirm number (not the "Orbitz locator code" that starts with PB) that I get immediately - on the screen after entering the credit card info - works to link on MDE.
BUT now that I'm thinking about it:
It is possible that I'm waiting 1 or more days to go to MDE and link at MDE (b/c I don't want overlapping reservations - always scared Disney will follow through on canceling both), so maybe that is the difference (guessing Orbitz has to upload the info to Disney somehow, and wouldn't be surprised if that isn't instant)? Anyway, I'm glad to hear of your experience, so I won't be worried if it happens to me. I save so much money on Orbitz (especially now using their Visa card) I'm willing to deal with extra steps.