I only used 14w30c & 14w31a, but I'm assuming this bug has been around since enchanting was changed.

Opening a world to LAN makes it to where you don't get a new enchantment after you enchant something. For example, the enchantment hint was "Silk Touch I." I chose that enchantment and the next three times it was "Silk Touch I." All three times I had my world Opened To LAN, however no one had gotten onto my world when I did so because I was using LAN for cheats. This wasn't just a lucky coincidence, I had the same enchantment hint, "Bane of Arthropods IV," on a book when I put it in. I enchanted one "Bane of Arthropods IV" book and the next time I looked the book had the same enchant hint. I had noticed, however, during the three times I enchanted the Silk Touch picks, the first and second time it was Silk Touch and Efficiency IV, and the third time it was plain Silk Touch.