  In this note we consider the moduli space of stable bundles of rank two on a
very general quintic surface. We study the potentially obstructed points of the
moduli space via the spectral covering of a twisted endomorphism. This analysis
leads to generically non-reduced components of the moduli space, and components
which are generically smooth of more than the expected dimension. We obtain a
sharp bound asked for by O'Grady saying when the moduli space is good.
