So, watching Captain America: Winter Soldier, I think I spotted a flaw regarding to Captain America's shield properties. There is a scene where Cap is fighting Winter Soldier and his henchmen alongside Falcon and Black Widow. One of the henchmen starts to fire with a minigun and Steve Rogers uses his shield to deflect the bullets and hit another henchmen.
But, watching this scene from Captain America: First Avenger, Howard Stark explains that the vibranium, the material from which the shield is made, is completely vibration absorbent. Then, Peggy Carter shoots at the shield and the bullets completely stop on impacting the shield.
There is some explanation on how the bullets were deflected in Winter Soldier movie?