Well, I replaced the voltage divider with a TLE2426 and got the same results. Everything looks fine on the bipolar circuit by itself. However, as soon as I connect the ground lead of my oscilloscope to the ground of the unipolar signal, the bipolar signal shifts back to 0-5V. It seems that the virtual ground of 2.5V goes to 0V as soon as I do this because the voltage potential across the ground pin and 1/2 voltage pin of the TLE2426 goes to 0. Is there something wrong with my circuit? If not, any other ideas?