  In recent years, a number of planetary systems have been proposed to orbit
evolved binary star systems. The presence of planets is invoked to explain
observed variations in the timing of mutual eclipses between the primary and
secondary components of the binary star system. The planets recently proposed
orbiting the cataclysmic variable system QS Virginis are the latest in this
on-going series of "extreme planets".
  The two planets proposed to orbit QS Virginis would move on mutually crossing
orbits - a situation that is almost invariably unstable on very short
timescales. In this work, we present the results of a detailed dynamical study
of the orbital evolution of the two proposed planets, revealing that they are
dynamically unstable on timescales of less than one thousand years across the
entire range of orbital elements that provide a plausible fit to the
observational data, and regardless of their mutual orbital inclination. We
conclude that the proposed planets around the cataclysmic variable QS Virginis
simply cannot exist.
