St. Josaphat himself was and is controversial, in fact one of the most contentious saints I've ever read about.
In October 1623 [St.] Kuntsevych ordered the arrest of the last priest who was clandestinely holding Orthodox services at Vitebsk, where Kuntsevych had a residence. Enraged at this, some Orthodox townspeople(along with Lithuanian Protestants) lynched Kuntsevych on 12 November. Witnesses of the event described it as follows:And in retaliation
The ringing of cathedral bells and the bells of other churches spread. This was the signal and call to insurrection. From all sides of town masses of people – men, women, and children – gathered with stones and attacked the archbishop's residence. The masses attacked and injured the servants and assistants of the archbishop, and broke into the room where he was alone. One hit him on the head with a stick, another split it with an axe, and when Kuntsevych fell, they started beating him. They looted his house, dragged his body to the plaza, cursed him – even women and children. ... They dragged him naked through the streets of the city all the way to the hill overlooking the river Dvina. Finally, after tying stones to the dead body, they threw him into the Dvina at its deepest.
Kuntsevych's canonization process began in the interval of the January Uprising of 1863–1865 against the Russian Empire and was "understood in many circles, including Polish, Russian, and Ruthenian circles, as a papal gesture of moral support for the insurgent Poles." A Russophile Ruthenian newspaper, Slovo (uk), published several negative articles about Kuntsevych. This antagonism to his canonization "makes sense within the context of the Russophile hegemony in Ruthenian public opinion" and was seen as insult to Imperial Russia. The Russian government responded, in 1875, with further Russification and forced conversion of the Eastern Catholic Chełm Eparchy, the last Eastern Catholic eparchy in the Russian Empire.Yet,
After numerous miracles attributed to Kuntsevych were reported to Church officials, Pope Urban VIII appointed a commission in 1628, to inquire into his possible canonization, which examined 116 witnesses under oath. Josaphat's body was claimed to be incorrupt five years after his death. In 1637, a second commission investigated his life and, in 1643, Josaphat was beatified. He was canonized on June 29, 1867 by Pope Pius IX.As in many of these East/West matters, it's complicated and blood boils to this day on both sides.
Bonus: My friend EMR posts more at Cream City