Tool disappearing until i reset my game after renaming it.

I wanted to rename my axe in a realm i joined and i go to the anvil. The anvil is already very low health. I put my axe in and type the name i want, and the anvil breaks and my axe is gone. I was very confused and frustrated. So i reset my game and then my axe is in my hotbar. I don't know why my axe went away.