Mary (mother of Jesus)
Differences in feasts may also originate from doctrinal issues—the Feast of the Assumption is such an example. Given that there is no agreement among all Christians on the circumstances of the death, Dormition or Assumption of Mary, the feast of assumption is celebrated among some denominations and not others.  While the Catholic Church celebrates the Feast of the Assumption on August 15, some Eastern Catholics celebrate it as Dormition of the Theotokos, and may do so on August 28, if they follow the Julian calendar. The Eastern Orthodox also celebrate it as the Dormition of the Theotokos, one of their 12 Great Feasts. Protestants do not celebrate this, or any other Marian feasts.

Q: On what date of the Julian calendar do Eastern Catholics celebrate the Domition of the Theotokos?
August 28