In order to land this plane (as most warbirds) you have to get it at an high angle of attack by combining some power with up elevator.

This induces an effect on some wings where the air moving over the top does not flow smoothly causing the raising aileron to become much less effective. you are then effectively only using one opposite aileron to raise it's wing.

This is generally due to little or lack of washout in the wingtip and/or not enough aileron control surface.

Remember on your trainer how if you where about to stall and you tried to use the ailerons it was very very sluggish? It's essentially the same effect only not as pronounced.

Hope this helps!