Using a representation in terms of a two-type branching particle system, we
prove that positive solutions of the system (u) over dot = Au + uv, (v) ov
er dot = Bv + uv remain bounded for suitable bounded initial conditions, pr
ovided A and B generate processes with independent increments and one of th
e processes is transient with a uniform power decay of its semigroup. For t
he case of symmetric stable processes on R-1, this answers a question raise
d in [4].