The microstructures of shock compressed metals and metallic alloys reveal tell-tale signs of plasticity. For instance, the residual microstructure of shock recovered metals and metallic alloys may reveal an increase in dislocation density, increase in twin density, stacking faults, etc. with increase in shock stress and pulse duration. Here we report the anomalous behavior of a chemically optimized and microstructurally stable bulk nanocrystalline copper-3at.% tantalum material for which the microstructure and residual hardness are insensitive to shock stresses ranging up to 34 GPa. These observations warrant more comprehensive studies on nanocrystalline materials.