I-spin and U-spin in $B \to K K \bar K$

Isospin symmetry is a useful approximation for studying $B$ meson decays to three kaons, $B\to KK\bar K$. U-spin symmetry, relating three body B decays involving charged kaons and pions, may be applied for tests of penguin dominance in $B\to KK\bar K$. We point out certain subtleties in treating these decays in these approximations, and discuss resulting uncertainties in determining the CP content of the final state in $B \to K^+K^-K_S$.