  A growing number of eclipsing binary systems of the "HW Vir" kind (i. e.,
composed by a subdwarf-B/O primary star and an M dwarf secondary) show
variations in their orbital period, also called Eclipse Time Variations (ETVs).
Their physical origin is not yet known with certainty: while some ETVs have
been claimed to arise from dynamical perturbations due to the presence of
circumbinary planetary companions, other authors suggest that the Applegate
effect or other unknown stellar mechanisms could be responsible for them. In
this work, we present twenty-eight unpublished high-precision light curves of
one of the most controversial of these systems, the prototype HW Virginis. We
homogeneously analysed the new eclipse timings together with historical data
obtained between 1983 and 2012, demonstrating that the planetary models
previously claimed do not fit the new photometric data, besides being
dynamically unstable. In an effort to find a new model able to fit all the
available data, we developed a new approach based on a global-search genetic
algorithm and eventually found two new distinct families of solutions that fit
the observed timings very well, yet dynamically unstable at the 10^5-year time
scale. This serves as a cautionary tale on the existence of formal solutions
that apparently explain ETVs but are not physically meaningful, and on the need
of carefully testing their stability. On the other hand, our data confirm the
presence of an ETV on HW Vir that known stellar mechanisms are unable to
explain, pushing towards further observing and modelling efforts.
