By the way as jxjxhwx states, waveform is not strange. Indeed quite typical, for example, for low power (i.e. low branch currents) folded cascode opamp.
If you quickly want to verify it please increase your branch currents as much as you can (take care of transistor regions) and see the corresponding result
Ringing is typical, but I seldom see this kind of ringing waveform in good designs.
If you say it's typical, could you give me some paper which show this kind of waveform ?