Mending enchant not working properly. Experience goes into level bar instead of mending tool.

So my friends and I have a realm together. One of my friends has a skeleton spanner and allows me to use it. It has a trident killer in it. While I was afk at his skeleton spawner, I had my mending 1, efficiency 5, Unbreaking 3 ax in my main hand. I took of my elytra because that is my only piece of armor with mending on it. I realized that my ax was getting mended much slower then it usually does. Then I realized that my experience bar was rising instead of my ax's durability bar.