After enchanting, collecting new xp restores my previous level

After doing about 10 enchantments on the enchanting table, bringing my player level from ~50 to 26, such that I could no longer do level 3 enchantments, I went up to my monster grinder and started hacking away. There may have been 30-40 skeletons&zombies that I slew. Upon collecting xp for it, I noticed my player level was right back up to 51-52.

This is occurring on my Realm.