Villager leveling up

I went to level up my armorer to try and get some diamond armor but I realized something. Even though I leveled him up, his level was the same and the experience bar was reset. I have proof that I had already done a level 2 trade but the bar was at zero as if I had just leveled him up (Instead of 4 iron it is 5 because I did that trade a lot). I tried this with a fletcher afterwards and the same thing happened. Please help!