from the IFV "Whats New":
Updates to deadlock state
In this release, the deadlock state property has been enhanced to check that the FSM cannot take any transition to the same state under any possible input combination.
This deadlock state is supported by all engines and results in an improved performance.
For complete information, see the section titled, "FSM Checks" in Chapter 10 of the Formal Verifier User Guide.
What is implicitly explained here is the fact, that any input, that can control the outgoing transition of a FSM state, is now allowed to stall the FSM in 13.1, resulting in a noDeadlock failure. It is now required from the user to analyze and decide if that scenario is possible in the intended system context or not. If not, the user may add a fairness constraint like "eventually! !stable(<input>) and reduce unfairness manually.