  It has been suggested that the prompt emission in gamma-ray bursts consists
of several components giving rise to the observed spectral shape. Here we
examine a sample of the 8 brightest, single pulsed {\it Fermi} bursts whose
spectra are modelled by using synchrotron emission as one of the components.
Five of these bursts require an additional photospheric component (blackbody).
In particular, we investigate the inferred properties of the jet and the
physical requirements set by the observed components for these five bursts, in
the context of a baryonic dominated outflow, motivated by the strong
photospheric component. We find similar jet properties for all five bursts: the
bulk Lorentz factor decreases monotonously over the pulses and lies between
1000 and 100. This evolution is robust and can neither be explained by a
varying radiative efficiency nor a varying magnetisation of the jet assuming
the photosphere radius is above the coasting radius. Such a behaviour
challenges several dissipation mechanisms, e.g., the internal shocks.
Furthermore, in all 8 cases the data clearly reject a fast-cooled synchrotron
spectrum (in which a significant fraction of the emitting electrons have cooled
to energies below the minimum injection energy), inferring a typical electron
Lorentz factor of $10^4 - 10^7$. Such values are much higher than what is
typically expected in internal shocks. Therefore, while the synchrotron
scenario is not rejected by the data, the interpretation does present several
limitations that need to be addressed. Finally, we point out and discuss
alternative interpretations.
