  The difference in the time dependent CP asymmetries between the modes $B -->
psi K_S$ and $B --> phi K_S$ is a clean signal for physics beyond the Standard
Model. This interpretation could fail if there is a large enhancement of the
matrix element of the $b --> u ubar s$ operator between the $B_d$ initial state
and the $phi K_S$ final state. We argue against this possibility and propose
some experimental tests that could shed light on the situation.
