  We present a theoretical analysis of quasiparticle poisoning in
Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting
leads. Taking into account finite-energy quasiparticles, we derive the
effective low-energy theory and present a renormalization group analysis. We
find qualitatively new effects when a quasiparticle state with very low energy
is localized near a tunnel contact. For $M=2$ attached leads, such "dangerous"
quasiparticle poisoning processes cause a spin $S=1/2$ single-channel Kondo
effect, which can be detected through a characteristic zero-bias anomaly
conductance peak in all Coulomb blockade valleys. For more than two attached
leads, the topological Kondo effect of the unpoisoned system becomes unstable.
A strong-coupling bosonization analysis indicates that at low energy the
poisoned lead is effectively decoupled and hence, for $M>3$, the topological
Kondo fixed point re-emerges, though now it involves only $M-1$ leads. As a
consequence, for $M=3$, the low-energy fixed point becomes trivial
corresponding to decoupled leads.
