  One of the most popular state-space reduction techniques for model checking
is partial-order reduction (POR). Of the many different POR implementations,
stubborn sets are a very versatile variant and have thus seen many different
applications over the past 32 years. One of the early stubborn sets works shows
how the basic conditions for reduction can be augmented to preserve
stutter-trace equivalence, making stubborn sets suitable for model checking of
linear-time properties. In this paper, we identify a flaw in the reasoning and
show with a counter-example that stutter-trace equivalence is not necessarily
preserved. We propose a stronger reduction condition and provide extensive new
correctness proofs to ensure the issue is resolved. Furthermore, we analyse in
which formalisms the problem may occur. The impact on practical implementations
is limited, since they all compute a correct approximation of the theory.
