A319 flight crew reports being informed in flight that hazmat has been incorrectly loaded. After return and aircraft swap hazmat is again loaded incorrectly. Error is caught prior to takeoff this time.

Narrative

We received an ACARS message recommending strongly we return to ZZZ because we had some dangerous goods materials loaded incorrectly. We returned to ZZZ without incident. All checklist items were handled and we landed after doing the overweight landing checklist; performance landing weight checklist; and the landing distance checklists. We touched down at 127 KIAS (VLS-128). Touchdown rate was 200 FPM. Touchdown weight was 139200 lbs. After landing; we taxied to the gate where we were told to proceed to the next gate and get a new airplane. We taxied out and at the hold short of Runway 32L/T10 we went to the hold pad because we couldn't get our final weights. After waiting for about 10 minutes we were contacted by Dispatch and told we had been loaded the exact same way that our original flight took off. After discussion with Dispatch; we went back to the gate and took on additional fuel and were finally loaded correctly without dangerous goods. We took off and landed without incident. My question is; how can a flight be loaded with dangerous goods incorrectly -- twice -- especially after the flight returned with loading problems?