  Typically, quantum superpositions, and thus measurement projections of
quantum states involving interference, decrease (or increase) monotonically as
a function of increased distinguishability. Distinguishability, in turn, can be
a consequence of decoherence, for example caused by the (simultaneous) loss of
excitation or due to inadequate mode matching (either deliberate or
indeliberate). It is known that for some cases of multi-photon interference,
non-monotonic decay of projection probabilities occurs, which has so far been
attributed to interference between four or more two photons. We show that such
a non-monotonic behaviour of projection probabilities is not unnatural, and can
also occur for single-photon and even semiclassical states. Thus, while the
effect traces its roots from indistinguishability and thus interference, the
states for which this can be observed do not need to have particular quantum
features.
