In standard ΛCDM, scalar perturbations generate only E-mode polarization and B-modes arise mainly from gravitational lensing of E-modes, so on CMB scales the EE and lensing-induced BB patterns are expected to be tightly linked and highly correlated in both amplitude and spatial structure, apart from well-understood noise and foregrounds (Zaldarriaga & Seljak 1997; Hu & White 1997). Planck and ground-based experiments, however, have reported hints that the observed EE and BB power, and especially their frequency and spatial correlations, show signs of partial decorrelation and subtle mismatches that are hard to reconcile with a single, perfectly coherent lensing-and-foreground model, thereby complicating the interpretation of B-modes and suggesting either more complex foreground and dust physics or departures from the simplest ΛCDM assumptions (Planck Collaboration XI 2020; BICEP/Keck Collaboration 2018).