  We show that for hadronic transverse energy $E_T$ in hadron-hadron
collisions, the classic Collins-Soper-Sterman (CSS) argument for the
cancellation of Glauber gluons breaks down at the level of two Glauber gluons
exchanged between the spectators. Through an argument that relates the diagrams
with these Glauber gluons to events containing additional soft scatterings, we
suggest that this failure of the CSS cancellation actually corresponds to a
failure of the `standard' factorisation formula with hard, soft and collinear
functions to describe $E_T$ at leading power. This is because the observable
receives a leading power contribution from multiple parton interaction (or
spectator-spectator Glauber) processes. We also suggest that the same argument
can be used to show that a whole class of observables, which we refer to as MPI
sensitive observables, do not obey the standard factorisation at leading power.
MPI sensitive observables are observables whose distributions in hadron-hadron
collisions are disrupted strongly by the presence of multiple parton
interactions (MPI) in the event. Examples of further MPI sensitive observables
include the beam thrust $B^+_{a,b}$ and transverse thrust.
