This is from the PvP Forums.
Hi. Blizzard, can you please fix this bug that causes my gear to break mid match or loses durability after the match. Even the tooltip loading screen when you enter world says that gear shouldn’t take durability points in pvp. This bug has unintentionally lost me arena matches. Ps: Voidchaos
Simply being in combat causes durability loss on gear over time. Using a piece of gear will also accrue durability losses - hitting an enemy with one, firing a bow, using a combat skill (including spells), blocking an attack, or taking a hit.
The loading screen tip states that “Your items do not suffer durability damage when you are killed by an enemy player” (emphasis mine). This is specifically in reference to the 10% of maximum durability loss triggered by most PvE deaths, and does not extend to the above (nor does it even suggest it would unless you’re deliberately misreading it with intent).