To reproduce the glitch you have to be in Survival gamemode and keep hitting a player that has creative gamemode until your weapon breaks (i've tested it using a golden and wooden sword).

In order to get the weapon back as new you can do the following:

• relog/rejoin the server

• open your inventory and click on the slot where the weapon was before it broke

You'll notice that the weapon you used to hit the player with has magically reappeared!

video: http://youtu.be/ZiF0U8XSvnE

Edit: When doing the same against survival players who ate a golden apple, the weapon returns instantly, but it will have a durability of 1