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.
Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.