In the pre-releases, I don't gain xp, no matter what

So basically i was playing on my survival world, and i was getting some xp for my diamond boots (enchanted book). after I used 17 levels to get feather falling 4 on my boots, i was at 1 level and i wanted to combine my 4 unbreaking 1 books to get an unbreaking 3 book. I decided to trade with villagers to get some xp, but when I traded, it made the xp sound effect, but it didn't give me any xp. I was worried and I relogged in, as well as restarting minecraft. It didn't work. and If I try to enchant anything, it says my levels are too low. Someone please help me.