We present a detailed study of GRB 090111 , focusing on its extra soft power-law photon index \Gamma > 5 at the very steep decay phase emission ( power-law index \alpha = 5.1 , steeper than 96 % of GRBs detected by Swift ) and the following peculiar X-ray re-brightening .
Our spectral analysis supports the hypothesis of a comoving Band spectrum with the the peak of the \nu F _ { \nu } spectrum evolving with time to lower values : a period of higher temporal variability in the 1-2 keV light-curve ends when the E _ { peak } evolves outside the energy band .
The X-ray re-brightening shows extreme temporal properties when compared to a homogeneous sample of 82 early flares detected by Swift .
While an internal origin can not be excluded , we show these properties to be consistent with the energy injection in refreshed shocks produced by slow shells colliding with the fastest ones from behind , well after the internal shocks that are believed to give rise to the prompt emission have ceased .