Note that, until Clinton, there was never any such thing as Presidential polls for a.) "job approval" and b.) "personal approval". Nor have there been any such bifurcated poll results since.
I suspect that, as Clinton's difficulties mounted, the media who commission these polls asked that the question be split in half, so as allow the public to vent its spleen in one answer and respond with a "well, duh, O.K., I guess" on the other.
After first focus group testing the concept, of course...