Hi again dvs7310
I've been playing around with this too.
And I've got the following itinerary to price up OK
So at the start, it has

• Europe via the Middle East to Asia, and

At the end it has:

• North America to Africa via the Middle East, followed by
• Africa to Europe (CMN) via the Middle East, followed by
• Europe to Middle East (CMN-DOH), followed by
• Middle East to Europe (DOH-ARN)

I think something else is going on the itineraries you've been trying.
Like you I tried itineraries starting in London, but they gave error messages about returning the country of origin when trying to fly DFW-JNB (trying to route me via LHR)
Another problem I had was caused by the tool making suggestions that resulted in the itinerary having more than 16 segments (for example into NRT, out from HND). Even after I fixed them all, on the final segment the tool said I had more than 16 segments (in that faint, hard to spot, orange-coloured text)
The trick I found that worked was to save the complete itinerary, log out of the tool, close its web browser window, and then reopen it.

dvs7310 - I'll send you a PM