  We analyse the multifield behaviour in D-brane inflation when contributions
from the bulk are taken into account. For this purpose, we study a large number
of realisations of the potential; we find the nature of the inflationary
trajectory to be very consistent despite the complex construction. Inflation is
always canonical and occurs in the vicinity of an inflection point. Extending
the transport method to non-slow-roll and to calculate the running, we obtain
distributions for observables. The spectral index is typically blue and the
running positive, putting the model under moderate pressure from WMAP7
constraints. The local f_NL and tensor-to-scalar ratio are typically
unobservably small, though we find approximately 0.5% of realisations to give
observably large local f_NL. Approximating the potential as sum-separable, we
are able to give fully analytic explanations for the trends in observed
behaviour. Finally we find the model suffers from the persistence of
isocurvature perturbations, which can be expected to cause further evolution of
adiabatic perturbations after inflation. We argue this is a typical problem for
models of multifield inflation involving inflection points and renders models
of this type technically unpredictive without a description of reheating.
