Please elaborate on this a little more. What I think I heard you say was that the Egyptian Copts were OK with Arab rule when it seemed (however briefly), like a power expanding at the expense of some pagan desert dwellers, but when the Caliphate resumed the offensive against the ERE, the Copts rebelled?
My view is that the Copts were wary but also happy to be free from Byzantium in the very earliest stages of the Caliphate whenever the Arabs where still seen as some odd Christian group or just an Arab force non aligned to Sassanid or Byzantine powers which would've appealed to Egypt. However, as the caliphate progressed in the next decades, its intentions to conquer Constantinople and invade Europe became too much for the Copts to betray their former masters and religion and thus the Coptic mutinies which ended the first Arab invasion of Byzantium.
Essentially the Copts at first were glad to be free but once they realized the Caliphates obvious distaste for Christian state structures, the Copts resisted and wished to return to Byzantine rule or at the very least wished to not fight Byzantium.