I thought Byzantine, Ukrainian, and Melkite Catholics used the Orthodox Calendar?
Well, I can't speak for the other Traditions, but Melkites in America definitely celebrated the Sunday of Orthodoxy today, as my children and I were part of the icon procession. Always a crowd pleaser for young children.
The priest at my first Melkite parish loved to point out that Melkites celebrate the same Eastern date as the majority of Christians in whatever place you're talking about. (He mentioned somewhere -- I don't remember where, maybe in Africa or the Middle East -- where the Eastern date is neither
of the two dates that we usually think of.)
Needless to say, it's not a matter of Rome saying: You have to celebrate Easter on such and such.