I could VERY well be wrong about this, but I have a vague memory from the L&E thread that the Orthodox don't agree with "something" about Transubstantiation, but I can't remember what it is.
Inasmuch as it means "Real Presence," i.e. True Body and True Blood of our Lord and Savior,it is in full agreement with Orthodoxy.
Eastern Orthodox, however, do not attempt to "explain" how God's Mysteries (Sacraments) happen.
In Eastern Orthodoxy, the priest asks the Holy Spirit to intercede and change mysteriously the blessed bread and wine into Body and Blood (epiklesis). In the Catholic Church, the epiklesis is invoked, but is less prominent, because the change is mediated by the priest, acting in the place of Christ.
With that we do not agree. Both traditions have always maintained the Real Presence, but the theory of transubstantiation is alien to Orthodox phronema (mindset).
They don't agree with the scholastic precision with which it is defined in the West and prefer not to attempt to verbalize a mystery.