Because OpenCoin has no plans in monetary policy and likely spontaneously changes their plans based on where the price is and where they would like it to go, it is probably prone to bubbles, even more so than Bitcoin, where the block chain relentlessly distributes according to an algorithm, no matter what.
Wherein by "prone to bubbles" what you really mean is "OpenCoin are deliberately trying to inflate a bubble in the hopes they will profit off the ignorant Bitcoin user".