  Using high-quality, broad-band afterglow data for GRB 091029, we test the
validity of the forward-shock model for gamma-ray burst afterglows. We used
multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND,
BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the
XRT onboard the Swift satellite. To explain the almost totally decoupled light
curves in the X-ray and optical/NIR domains, a two-component outflow is
proposed. Several models are tested, including continuous energy injection,
components with different electron energy indices and components in two
different stages of spectral evolution. Only the last model can explain both
the decoupled light curves with asynchronous peaks and the peculiar SED
evolution. However, this model has so many unknown free parameters that we are
unable to reliably confirm or disprove its validity, making the afterglow of
GRB 091029 difficult to explain in the framework of the simplest fireball
model.
