That bug is when you use / tool (I used / tool deltree in the Neather with a diamondpicaxe) and when I click on my chest to open it. It will repair my diamond picaxe to full level.

//osky2918 from SWE

just in the nether? how about multiworlds (if you have any)
also make sure it's not client side (durability should stay the same
if you log out and in)
and that you don't have anything like worldguard's disable durability on

Yes, I had worldguard's disable durability on, but is not this option is accepted to any location on the map (s) or just inside wg protection.

disable durability will always restore tools' durability whenever it
gets triggered no matter where you are, as it's a config option not a
region flag or something like that