In this paper, two things are done. (i) First, it is shown that any global
symmetry of a gauge-invariant theory can be extended to the ghosts and the
antifields so as to leave invariant the solution of the master-equation (before
gauge fixing). (ii) Second, it is proved that the incorporation of the rigid
symmetries to the solution of the master-equation through the introduction of a
constant ghost for each global symmetry can be obstructed already at the
classical level whenever the theory possesses higher order conservation laws.
Explicit examples are given.Comment: 12 pages, no figures, late
