Small-angle neutron scattering and optical birefringence were used to study the disordering transition of a cylindrically ordered block copolymer material. It was found that the disordering temperature of shear-oriented "single crystals" was 62 degrees C, while that of imperfect, granular samples formed under quiescent conditions was 49 degrees C. In sheared samples where the imperfections were partially removed, coexistence of ordered and disordered regions was observed at temperatures between 49 and 62 degrees C.