I've seen this occur a few years back with a wing tank pump fault. From memory the ECAM called for the faulty pump to be turned off and cross feed opened. This resulted in the same situation as hossein. At top of climb we had a 500 kg imbalance with the heavier wing being on the side with 2 good pumps. Never did find out the actual reason. I have always thought it could possibly be due to system plumbing ( pipe diameters, junctions etc) causing a Venturi effect and sucking the fuel from the side with only one pump operating to the other. Part of the reason for this thought is the inconsistency with the fuel temperatures. In hossein's case the left outer is a lot warmer which (if both IDGs are running well) would indicate that more fuel is returning from the engine. The right outer temp is probably colder because lower fuel pressure within the engine and minimal fuel returning to tank.
Please note this is all assumptions but the best I could come up with. I also don't think you could test this in a sim I think you would have to check it in a real aircraft.
Any engineers out there have any answers?