Durability of Golden Swords occasionally dropped by Zombie Pigmen is not random (always 25)

I spawned a bunch of Zombie Pigmen (about maybe a hundred), then I killed them and noticed that each dropped golden swords have the same durability of 25 hits. (see picture "Durability").
I did the same with Skeletons (about maybe fifty) and as you can see in picture "Correct", here, the randomness in the durability of dropped gear works fine.
EDIT : still a concern in 1.8.1-pre3. See new picture