First, although I've been a member since 9/18, it still took several days to authorize me to use the forums. That's beyond frustrating.
Second, I saved RP items for weeks in prep for the X2 RP event. When I went to upgrade items, I burnt through 10 preservation stones in a row. Not on a 50% item. But on a 90% item. And it wasn't only me. Lots of other people reported this problem. I've never lost a single pres stone on a 90% item. 10 in a row suggests a design. I strongly suspect you fudged the odds so that people will spend Zen on pres stones.
Third, I don't mind spending money on a game. But I do mind it when you fudge mechanics to try and motivate me to spend money.