Mending on tools doesnt work while wearing armor with mending

When Im wearing armor with mending on it my tools don't get any xp even though they have mending too. But when I take of my armor my tools start to receive xp. My armor doesnt need to be mended anymore and the xp I get goes towards my levels when holding a tool with mending. So basically when I have repaired mending armor and want xp for my mending tools it just goes to my xp bar for levels.