May I add that it is the opinion of the OO Church that councils confirm the already existing truth, not creating new "truths." Anything else like canons or anathemas can be tested if it wasn't accurate. However, "infallibility" of councils, if I was to define it, is no different than "infallibility" of the Bible. Whereas the spirituality and dogma they teach are without question, the details around them may or may not be questioned.
While we do hold three ecumenical councils, I feel we hold two more that has ecumenical status that we accept as dogmatically and spiritually infallible, but in detail can show that Chalcedon, Flavian, and Leo may be withdrawn from anathema. Canons also have to adapt to changing times and cultures. I think even the EO's agree that not all canons that have been written in the ecumenical councils apply today anymore.
I think it's more accurate to say that the councils are indeed infallible, just not inerrant.