United is letting me book a crazy itinerary and I have a short 1 hr and 15 minute connection at JNB. I am flying MRU - JNB - LHR - GVA - YUL on one ticket all through Star Alliance. The MRU and LHR segments are on SAA. I believe that I can A) Check bags through to the final destination and B) Not have to go through customs since I am going from International to International. Although, from what I have researched it seems that the SAA Flight departs out of Terminal B and I arrive in Terminal A from Mauritius. Is there international transfers from Terminal A to B?

Thank you all.