  Realistic many-particle systems dynamically exchange particles with their
environments. In classical physics, small variations in the number of
constituent particles are commonly considered practically irrelevant. However,
in the quantum mechanical context, such and similar structural variations are
generically taxed due to the so-called Entanglement Relativity. In this paper
we point out difficulties in deriving master equation for a subsystem of an
alternative partition of the closed quantum system. We find that the
Nakajima-Zwanzig projection method cannot be straightforwardly used to solve
the problem. The emerging tasks and prospects for the consistent foundations
are examined.
