  The discrepancy between Theta^+ photoproduction on proton vs. deuteron can be
resolved if the photon couples much more strongly to K^+K^- than to K0 K0bar as
indicated by the experimentally observed asymmetry between gamma p -->
Lambda(1520) K^+ and gamma n --> Lambda(1520) K_s. Significant
signal-background interference effects can occur in experiments like gamma N
--> Kbar Theta^+ which search for the Theta^+ as a narrow I=0 resonance in a
definite final state against a nonresonant background, with an experimental
resolution coarser than the expected resonance width. We show that when the
signal and background have roughly the same magnitude, destructive interference
can easily combine with a limited experimental resolution to completely destroy
the resonance signal. Whether or not this actually occurs depends critically on
the yet unknown relative phase of the I=0 and I=1 amplitudes. We discuss the
implications for some specific experiments.
