  A Feynman path integral analysis of a two-neutrino-flavour electron
appearence experiment following pion decay at rest recovers the standard
oscillation phase, revealing an important contribution from the decay amplitude
of the pion as well as an error in previous similar calculations by the present
author. In the calculation, path amplitudes for different neutrino mass
eigenstates add coherently, but no putative `neutrino flavour eigenstates' are
invoked.
  It is shown that the coherent production of the latter states is incompatible
with the measured values of $\Gamma(\pi \rightarrow {\rm e}\nu)/\Gamma(\pi
\rightarrow \mu \nu)$ and the PMNS matrix elements. Application of the path
integral approach to other two-path quantum interference experiments is
compared with that to neutrino oscillations, and other treatments of the latter
in the literature are discussed.
