It has long been puzzling that water nanodroplets undergo simultaneously "supercooling' at freezing and "superheating" at melting. Recent progress (Sun et al. J. Phys. Chem. Lett. 2013, 4, 2565, 3238) enables us to resolve this anomaly from the perspective of hydrogen bond (O:H-O) specific heat disparity. A superposition of the Specific heat eta(x)(T) curves for the H-O bond (x = H) and the O:H nonbond (x = L) defines two intersecting temperatures that form the ice/quasi-solid/liquid phase boundaries. Molecular undercoordination (with fewer than four nearest neighbors in the bulk) stretches the eta(H)(T) curve by raising the Debye temperature Theta(DH) through H-O bond shortening and phonon stiffening. The eta(H)(T) stretching is coupled with the eta(L)(T) depressing because of the Coulomb repulsion between electron pairs on Oxygen ions. The extent of dispersion varies with the size of a droplet that prefers a core-shell structure configuration the bulk interior and the skin. Understandings may open an effective way of dealing with the thermodynamic behavior of water droplets and bubbles from the perspective of O:H-O bond cooperativity.