Frederic Bouvier:

I just discovered this : state() is not valid when _level==0,
because it is doing:
{ return _state_stack[_state_stack.size() - 1]; }
and is returning a wrong index fetch ( 0 - 1 ) == -1

Moreover, st is not used when _level==0 so the line can be moved
to a safer place.

simgear/props/props_io.cxx

@@ -133,7 +133,6 @@ checkFlag (const char * flag, bool defaultState = true)
 void
 PropsVisitor::startElement (const char * name, const XMLAttributes &atts)
 {
-  State &st = state();
   const char * attval;
 
   if (_level == 0) {
@@ -160,6 +159,7 @@ PropsVisitor::startElement (const char * name, const XMLAttributes &atts)
   }
 
   else {
+    State &st = state();
 				// Get the index.
     attval = atts.getValue("n");
     int index = 0;