  It is argued that the recent Belle data, consistent with no activity in the
spectrum of the $B^* \bar B + B \bar B^*$ pairs at the mass of the $Z_b(10650)$
resonance, imply that the part of the interaction between heavy mesons that
depends on the total spin of the light quark and antiquark is strongly
suppressed. In particular this part appears to be significantly weaker than can
be inferred from pion exchange. If confirmed by future more detailed data, the
symmetry with respect to the light quark spins, in combination with the heavy
quark spin symmetry, would imply existence of four additional $I^G=1^-$
resonances at the thresholds for heavy meson-antimeson pairs.
