Stacked images of the transformed Stokes parameters Q_r (top) and U_r (bottom) for SMICAE-mode hot spots. The rotation of the plane of polarization will act to leak the signal from Q_r into U_r. The quadrupole pattern in the bottom plot is related to subpixel effects (Planck Collaboration XV 2014; Planck Collaboration XI 2016); fortunately, our results are insensitive to this feature, because it disappears in an azimuthal average (see Sect. 5.1).