Cash Shop 90% OFF event

Could someone link to the announcement about this event, my Google skills seem poor?
I went into CS on one character (after taking so long to get in that I thought the game would crash) and there were several items 90% off.
I bought a permanent persion cat package for under 2k, and as soon as I did that, all the items went back to their regular price.
I went back into CS on other chars, but there were no more 90% off items. Tried another account, and saw nothing (but no NX on that account anyway).
Is this a random thing, once per account, or once per day, or what?

First purchase on an account that never bought anything in the Cash Shop before.
Which is why it went away after you bought one thing, and wouldn't show up on other chars on the same account.
As for the other account, I assume you bought something on it, sometime in the past.