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The recent discoveries of the bottomonia states h_b(1P) and h_b(2P) confirmthe quark model prediction, already verified in the charmonia sector, that thehyperfine splitting of P-wave mesons is very small. The striking agreement issomewhat surprising because the non-relativistic result, for which thesplitting is zero, may be modified due to large mass shifts from coupling toopen flavour meson pairs. This paper is based on the observation that in mostmodels hyperfine splitting remains small despite what are in many cases largemass shifts. This effect is shown to be a generic feature of models in whichthe coupling is driven by the creation of a spin-one pair.

How the small hyperfine splitting of P-wave mesons evades large loop corrections