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Experiments with ultracold neutrons (UCN) in bottles reveal that the probability of UCN losses at single collision with the bottle walls is of two order of magnitude higher than it is expected on theoretical grounds. In attempts to explain this anomaly it was supposed that the neutron is described by a wave packet that contains plane wave components with high enough energy to propagate over the potential barrier. Then the losses can be ascribed to the probability of penetration through barrier in non tunneling fashion that is proportional to part of the energy spectrum which is shared by high energy components. To forbid the independent propagation of high and low energy components of the wave packet it is necessary to suppose that the packet is the neutron's immanent wave function which is not spreading with time.