Electrical Engineering - TIA output goes beyond rails

I was experimenting with a transimpedance amplifier and a photodiode, the circuit was the following: Image_alt_text

Input current was initially calculated to be 500nA, which would produce -2V output. Current source was a photodiode combined with a laser with regulated power. Responsivity of the particular wavelength was known, and it seemed to give expected results.

As I turned the power higher on the laser, I expected the opamp output to saturate close to the power rail, as can be seen in the circuitlab simulation. However, instead, the opamp output seemed to follow below the negative rail, down to -4V (I did not put in more light). Afterwards, when power was reduced, opamp seemed to return to normal operation, I don't think it was damaged. This made me wonder, since photodiode is a current source forcing current through R1, what happens when opamp's output would reach the negative rail? How is it possible to go below the negative rail? What would happen to the extra photons the photodiode receives?

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TIA output goes beyond rails - How does it work?

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