I have the same issue. Replaced the O2 sensors as well and same crap happened. I myself will be replacing the pre-cat. That MIL is a bunch of poo. It eliminates the CEL, yippie, but if it IS a serious problem, guess what, you would find out the hard way.
Many people claim that they have driven their car for 40k miles with the CEL on and they had no issues. So might be just a faulty reading, but I don't like taking chances.