  Based on the description of unstable $K_{L,S}$ particles in quantum field
theory (QFT), we compute the time-dependent probabilities for transitions
between asymptotic states in $\tau^{\pm} \to [\pi^+\pi^-]_K\pi^{\pm}\nu$
decays, where the pair $[\pi^+\pi^-]_K$ is the product of (intermediate state)
neutral kaon decays. Then we propose a definition of $\tau$ decays into $K_L$
and $K_S$ states, which reflects into the cancellation between their CP rate
asymmetries, thus solving in a natural way the paradox pointed out previously
in litterature. Since our definition of $K_{L,S}$ final states in $\tau$ decays
is motivated on experimental grounds, our predictions for the integrated CP
rate asymmetries can be tested in a dedicated experiment.
