cocos2d x – Cocos2dx – how can box2d not get confused?

Player Box2d

auto playerbody = PhysicsBody :: createBox (sp-> getContentSize ());
playerbody-> setGravityEnable (false);
// playerbody-> setDynamic (false);
sp-> setPhysicsBody (player);

item box2d

auto ItemBody = PhysicsBody :: createBox (item-> getContentSize ());
ItemBody -> setGravityEnable (false);
ItemBody -> setDynamic (false);
item-> setPhysicsBody (ItemBody);

When moving these two boxes can move confused. How is that not?
Sorry for my bad English. many thanks