So, in Survival, I have a Iron Sword at exactly half durability (175/250). However, the durability bar disagrees. It shows that the durability is more than half.
To reproduce:
1. Get an Iron Sword through any possible means with a durability of 175/250.
2. Observe the durability bar. =D
(As a side note, the world was created in 1.8.2-pre4.)
250 divided by 2 is 125, not 175.