  We exhibit a pseudoeffective R-divisor D_\lambda on the blow-up of P^3 at
nine very general points which lies in the closed movable cone and has negative
intersections with a set of curves whose union is Zariski dense. It follows
that the diminished base locus B_-(D_\lambda) = \bigcup_{A ample}}
B(D_\lambda+A) is not closed and that D_\lambda does not admit a Zariski
decomposition in even a very weak sense. By a similar method, we construct an
R-divisor on the family of blow-ups of P^2 at ten distinct points, which is nef
on a very general fiber but fails to be nef over countably many prime divisors
in the base.
