When I attempt to run a simulation with a testbench created by HDL Bencher, all "X"s are reported in the output. The same situation occurs when I set both the Input Setup Time and the Data Valid to be "1".
ModelSim does not report any violations in the simulation, even though the "X"s are propagated throughout the simulation.
This problem occurs when the Input Setup Time is changed to "1" and the Output Valid After Time is also changed to "1" -- the model is not able to run correctly and propagates the "X"s.
To work around this issue, change the Input Setup Time and the Output Valid After Time to be "4".
In a future software release, the model will report a warning when the "X"s are propagated.