  We report a serious kinematics problem in the bremsstrahlung photon part of
the order-$\alpha$ outer (model independent) radiative correction calculations
for those neutron (and nuclear beta) decay observables (like electron-neutrino
correlation parameter measurement) where the proton (recoil particle) is
detected. The so-called neutrino-type radiative correction calculations, which
fix the neutrino direction in the bremsstrahlung photon integrals, use 3-body
decay kinematics to connect the unobserved neutrino direction with the observed
electron and proton (recoil particle) momenta. But the presence of the
bremsstrahlung photon changes the kinematics from 3-body to 4-body one, and the
accurate information about the recoil particle momentum is lost due to the
integration with respect to the photon momentum. Therefore the application of
the abovementioned 3-body decay kinematics connection for the radiative
correction calculations, rather prevalent in the literature, is not acceptable.
We show that the correct, so-called recoil-type radiative correction
calculations, which fix the proton (recoil particle) momentum instead of the
neutrino direction and use rather involved analytical, semianalytical or Monte
Carlo bremsstrahlung integration methods, result usually in much larger
corrections than the incorrect neutrino-type analytical methods.
