Run the model through the impasse that will appear, and compare your trace with Trace 5.
Do this at various watch levels. If you wish to know which rules will fire, use the debugger's Monitor matchSet window (or you can use the command matches to display the current match-set). To step at a finer grain through the program, use the e command.
To understand this impasse, you will have to see the preferences that are available for the operators in S1. You can see the preferences for operators with the previously covered preferences command (or use gui's Monitor Preferences window).
Run ahead a decision cycle and try the command again, to see what's going on. This can be repeated if necessary.