Carpatho-Rusyn immigrants arrived in America as Greek Catholics. They had bad relations with the Hungarian Roman Catholic bishops in the old country, and soon discovered that the Irish bishops in the USA were going to be even worse, so a movement arose to return to Orthodoxy; both Carpatho-Rusyns and Galicians participated in this movement, thus providing the demographic backbone of the Russian jursidictions in the northeastern US when jursidictional pluralism arose after the First World War.
However, almost immediately these congregations transferred their allegiance to Russian bishops, their own traditional religious culture began to be undermined. The process intensified with the arrival of a new wave of immigrants from Russia, refugees from the Bolsheviks. The Rusyns were uneducated peasants who became coal miners and steel mill laborers, and spoke an old-fashioned dialect in some respects antedating the split between Russian and Ukrainian and decorated by words of German, Hungarian, Romanian, and even Arabic origin; the new refugees were aristocrats and intellectuals (who had the resources to escape the Bolsheviks), and had nothing in common with the Rusyns culturally. So the Rusyn culture was suppressed on the pretext that any differences between it and Russian culture were Latinisms, corruptions that had arisen in the Unia.
In truth, there *were* a number of such Latin corruptions; there were also many elements representing old Orthodox traditions that had been lost by the Russians centuries earlier. Almost no one had the knowledge to discriminate between these, and so all the 'Rusyn peculiarities' were replaced by 'correct' Russian practice.
One result of this was the many Uniates who might otherwise have joined the move back to Orthodoxy preferred to stay where they were so as not to lose their ancestral traditions (and subsequently were subjected to much worse latinization than anyone dreamed of in the 1920s).
Another is that the second wave of Rusyns to return to Orthodoxy, in the 1930s, avoided Russian bishops and instead took refuge under the omophorion of the Patriarch of Constantinople. When the cultural traditions that they sought to preserve in this way are mentioned, Prostopinije always stands high on the list.
Recordings of Prostopinije are limited. The most readily available are those of English settings by Prof. J. Michael Thompson of the Byzantine Catholic Metropolitan Cantor Intstitute. Prof Thompson uses the Bokshai collect of 1905 as his source, and steers a middle course between watering down the melodies to accommodate the English text easily (as was done several decades ago) on the one hand, and preserving the melodies at the expense of ignoring the stress accents of the English text (as was done in reaction to the oversimplified versions formerly in circulation). These are professional choral setting sung by trained choirs, and not documentary recordings of congregational singing.
Some decades ago, a 10-inch 78 rpm record of the Divine Liturgy in Slavonic was issued by Michael Hilko, the cantor and choir director of St Peter and Paul Church in Passaic. Prof Hilko was a Russian patriot politically and had thorough professional musical training, but unlike most Russian choir directors he recognized the value of Prostopinije and arranged it for his choir, using the version preserved in the oral tradition of his parish.
A set of instructional records, also in 10-inch 78 rpm format, was issued in then Czechoslovakia, along with the Papp Irmologion of 1970 (a revision of the Bokshai book of 1906). These have a *lot* of Prostopinije sung solo by a Greek Catholic cantor of Preshov, Nikifor Petrashevich. They were reissued in the United States.
Traditionally, Prostopinije is sung 1) in unison (of course, a real congregation of men, women, and children is not singing literally in unison);
2) in two parts, in parallel thirds--what is called _samojilka_ singing in its simplest form;
3) in so-called 'natural harmony,' which however does not have here the textbook meaning of triadic harmony in accord with Western musical theory. Recently, transcriptions of such singing have been posted to the Prostopinije list (Yahoo Groups), made from tapes of a Pascal service in Slavonec by the daughter of the cantor who was leading the singing recorede on the tapes. There are four parts: the upper two are in parallel thirds, as described above; the third is almost all on the key note, and this may be what sounded like ison as described in this thread; the fourth was a simple bass employing only a few notes. There is no useful discussion of this sort of singing as far as I know, and these new transcriptions are the first I have encountered made from documentary recordings.
Related to Prostopinje: the Galician chant, which is better provided with notated books; and the Bukovina chant, with one book and that entirely unobtainable. But manuscript irmologia containing a related repertory show that the Prostopinije is part of a tradtion once prevalent in all of Ukraine and Biealrus'; in most of its former territory, this tradition has suffered the same fate as the Prostopinije in Russian jursidictions in the USA.