When loading a trace in the simulator, no element of the trace is selected and the list of enabled transitions and the variables panel is empty. Upon selecting the first element of the trace, the list of enabled transitions is initialised. However, the variable panel is still empty. The expected result would be to see the variables of the state.
This is actually just a symptom of a more serious problem: If the transition in the list of enabled transitions is deselected, then clicking states in the trace (as opposed to transitions) will not update the state that is visualised in the simulator.
Except for the fact that the first element is not selected upon loading a trace, this fault explaines the phenomenon described above.
Fixed on the trunk from rev. 1711.