Slight Annoyance

Hey Riot, I'm one of probably a few players who actually makes and uses the item sets in the profile, and I've had my lists completely disappear on me twice now, and on the same computer. I put a decent amount of time into them, and would really like to know why this happens, if it's preventable, and whether or not I can get back all the lists I've already made. I don't know if they go away as a new patch comes in, or just after a certain period of time, but I'd really like it if this didn't happen anymore.

Thank you for your time.

Invictus