So what if an IOU is involved in an exchange? I'm not going to have that IOU randomly substituted for something else because OpenCoin Inc places having a flawed system that somewhat works over not making me lose money.
And again you change topics and are back claiming IOUs are substituted randomly. A balance shifting between entities you've told the system are interchangeable is not randomly.. If you don't want your balances to shift, trust only one gateway. Which is the recommended use case.