I guess this proves that they have a long indigenous tradition in copying Greek manuscripts... Also, they don't use the Byzantine diacritics (accents). IIRC Coptic uses lots of affixes with grammatical function, so that might explain what was in the mind of the Egyptian scribe who copied such a text, who might not have been proficient in Greek. It would be interesting to know just how long Greek survived as current liturgical language at Alexandria after the Arab conquest.
The irregular spelling also reflects modern Greek pronunciation. "KAI" is often "KE" while in the text you quoted "COI" becomes "CI".
I was also thinking the affixes might be due to the scribes treating Greek as if it was Coptic, though I assume some of it also has to do with simple editorial error. The beginning of the Resurrection Apolytikion for Pl. 1st Tone, for example, is often written as "Ton sina anarchon" in Coptic books, rather than "Ton synanarchon".
I find the use of Greek in the Coptic liturgical tradition really interesting. I think it in some ways is a good model for liturgical celebration in other languages too: the longer prayer translated into the vernacular while repetitive responses and popular hymns remain in the original.