We report on NMR evidence about a novel effect in La1-xCa xMnO3+δ systems with cation deficience. We show that in the low-Ca-doping regime, these systems exhibit a very strong hyperfine field at certain La nuclear sites, which is not present in the stoichiometric compounds. Comparison of our NMR results with recent X-ray absorption data at the Mn K-edge, suggests the formation of a spin-polarized hole arrangement on the 2p oxygen orbitals as the origin of this effect.