Large anomalies have been observed in the Bragg beam produced by Be (101), Be (103), Be (100), and Be (0002) monochromators on the MTR crystal spectrometer. Instead of a smooth spectrum characteristic of a Maxwellian distribution of neutron velocities, many large dips were found. These dips appear to be caused by extinction of the beam due to Bragg reflection by planes in the crystal other than those supplying the Bragg beam to the spectrometer. Calculations of the angles at which such competition can be expected have resulted in the identification of the planes responsible for the principal dips. To establish that these anomalies are due to crystal properties, spectra produced by the (200), (220), and (240) planes of NaCl were also examined. Although a few extinction dips were observed, these were far smaller in number and amplitude than those found in Be, due to the simpler crystal structure and lower reflectivity of NaCl. These effects require careful consideration in high-accuracy experiments with the crystal spectrometer, particularly in the measurement of reactor spectra.