Me too; but I think Campion is right: We'll have to get to heaven and ask St. Jerome himself.
Pope Benedict XVI speaks of "God is the Rock" as follows:
The faith should keep us in a constant attitude of humility before God, indeed of adoration and praise. In fact what we are because we are Chistians, we owe solely to Him and to his grace. Our radical belonging to Christ and the fact that "we exist in Him" should give us an attitude of total confidence and immense joy. Our Christian life therefore stands on the most stable and safe rock imaginable. And from this rock we draw all our strength.
It does indeed declare the Deu 32:4 Name for God, God is the Rock! So where the translation evidently failed, the truth of the matter did not.
Praise God!!!
And truly if this investigation cannot tell us what happened in the translation, then I will indeed ask St Jerome when I get there.