I've noticed that in some siddurim in the prayer "El Adon" the last line has the order of the angels switched; that is, they say:
"seraphim, chayot, v'ophanei hakodesh"
"seraphim, ophanim, v'chayot hakodesh",
and yet all siddurim by Shema say "ophanim v'chayot hakodesh". So my question is what is the origin of this phrase (both by Birchot Kriat Shema and "El Adon") and why do some siddurim (e.g., Chabad) have the order of the melachim "flipped"?