propExploration test failure

[bolt12]

      propExploration:                         FAIL (743.31s)
        *** Failed! Falsified (after 52 tests and 76 shrinks):
        AreNotEqual
        Shrink2 {getShrink2 = Tasks [Task [WhenSet 0 0],Task [],Task [ThrowTo 1],Task [WhenSet 0 0,ThrowTo 1],Task [ThrowTo 1],Task [ThrowTo 1,WhenSet 1 1]]}
        Schedule control: ControlAwait [ScheduleMod (RacyThreadId [5],2) ControlDefault [(RacyThreadId [4],0),(RacyThreadId [4],1),(RacyThreadId [3],0),(RacyThreadId [3],1),(RacyThreadId [3],2),(RacyThreadId [2],0),(RacyThreadId [1],0),(RacyThreadId [1],1),(RacyThreadId [1],2),(RacyThreadId [4],2),(RacyThreadId [4],3)]]
        Thread {5} (5) delayed at time Time 0s
          until after:
            Thread {1}
            Thread {1} (1)
            Thread {2}
            Thread {3}
            Thread {3} (3)
            Thread {4}
            Thread {4} (4)

        (...)

        InternalError "assertion failure: Thread {4} not runnable"
        assertion failure: Thread {4} not runnable
        Use --quickcheck-replay=564358 to reproduce.
        Use -p '/propExploration/' to rerun this test only.

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