IOC sounded like all or nothing to me. I am still learning the less obvious order settings, and I expected the BTC entry to fill completely or cancel completely. What I got was a partial fill.
The BYDFi order history showed that the available quantity had filled and the remainder had been canceled. That is what Immediate or Cancel asks for. It takes whatever can execute right away. FOK is the instruction that requires the full quantity to fill immediately or cancels the whole order.
I had mixed up two names that sounded close enough in my head. The partial position was small, so I closed it and went back to the order settings. IOC was working. My translation of it was the broken part.