One significant problem of the conversion to the Revised Julian Calendar, has been the resulting mixed calendar use within the Eastern Orthodox Christian Church. The situation is attributable to the fact that the conversion, which began in 1924, was not effected in a conciliar manner-on a pan-Orthodox basis. There was the 1923 Pan-Orthodox Congress which was attended by a few representatives of several, and not all, of the Holy Orthodox Churches, which was convened by the Ecumenical Patriarchate at The Phanar in Constantinople, and recommended the conversion. But the change was not agreed to by the Holy Synods of all of the Holy Orthodox Churches. It was the reformist government of Greece that chose to convert the nation's civil calendar to the Gregorian Calendar, which by that time had been adopted by Western nations. Then, the Greek government pressured the primate of the Church of Greece to change the church's calendar. One of the primary causes of the government's insistence was that the government felt that the Greek populous would demand that Greek Independence Day, March 25th, had to occur on the same day as the Feast of the Annunciation to the Theotokos, as it was in 1821, when Bishop Germanos of Old Patras proclaimed the revolution, following his having celebrated the Divine Liturgy for the Annunciation Feast Day. Being dependent on the government's financial support, the Archbishop of Athens, who only a few years earlier had chaired a special commission to examine the calendar question for the Greek Holy Synod, and issued a report that indicated that a conversion could only be accomplished on a pan-Orthodox basis, under the leadership of the Ecumenical Patriarchate, pressured the Ecumenical Patriarchate to make the conversion. The Patriarchate of Constantinople was in turmoil due to the change in governments from the Ottoman's and the Kemalic Republic and was likewise substantially dependent on the Greek government's financial support, owing, at least in part, to the population exchange between Turkey and Greece. (Transfer of church owned properties in the prior century to the government was what had/has created this dependence on the Greek government.) The Ecumenical Patriarchate obliged, converting to the so called Revised Julian Calendar, which reverts to the Julian Calendar for the Paschal Cycle of movable feasts. But as the change wasn't agreed to by any forum of the Holy Orthodox Churches, we are left with the mixed calendar use among the Churches, "some feast, while other fast," as Old Calendarists assert.
The calendar conversion and the involvement of the Holy Orthodox Churches in the ecumenical movement, has also caused the so called Old Calendarist, or traditionalist, separation. These separated Old Calendarist Churches seize upon a canon, that calls the faithful and the clergy to "wall [themselves] off," from bishops who preach false teaching. Therefore, today, we have the Holy Orthodox Churches using both calendars, (even within each church, like the Ecumenical Patriarchate, which led the conversion, while nearly all of the monasteries on the Holy Mountain, Mt. Athos, which is under its jurisdiction, retain the old calendar); and we have the Old Calendar schism, churches which have voluntarily separated from the Holy Orthodox Churches. These separated churches consider the old calendar, the Julian Calendar, to have become sanctified through its use by the church.
This situation is a lesson for those today who recently have advocated for the convening of the Holy and Great Synod (Council) of the Orthodox Church, which has been in planning stages for over 81 years, before a consensus is achieved on the issues it will address, arguing in favor of majority decision making, instead of general consensus.