Migration of residual pores in partially sintered 8 mol% yttria-stabilized zirconia under an electric field was investigated. To avoid shrinkage via sintering, Ar-filled bubbles introduced to dense ceramic were also studied. Pores/bubbles were found to migrate against the field, e.g., under 1.9 V at 875°C, a temperature when cation diffusion is supposed to have frozen according to the prevailing consensus. Pore/bubble movement left contorted grains in some samples, but not at lower temperatures and higher fields when they apparently pass through grain boundaries without causing any visible distortion. These results are explained by a surface diffusion model and a temperature-pore-size map that delineates two distinct modes of pore/boundary pinning and breakaway. The implications of these results to solid oxide fuel cells and electrolysis cells are explored.