We report an anomalous destruction of cholesteric blue phases I and II upon photopolymerizing, a liquid crystal mixture composed of mono- and diacrylate monomers. The platelet texture characteristic of the blue phase collapsed when the sample was irradiated by a weak UV light source, while Usual freezing of both blue phases I and II was obtained upon photopolymerization by a stronger light source. The phase destruction seems to be reflecting the robustness of the cubic lattice structure against external purterbations.