Hmm. I'm not sure. While the middle east is considered part of africa you're NOT returning to the same country you left from and IIRC it's permitted under the rules (because they only stipulate 1 transatlantic, trans siberia or transpac crossing). Run it by your prospective T/A or airline and ask if they would book it. I think it would be OK because you have no direct way to get from JNB->CAI on Star without going through Europe.
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RichardMEL, UA 1K
A Star Alliance Member.