create C++ application with code like:

int main(int argc, char** argv) {

    int j = 0;
    int i = 0;
#if 0
    commented out code which
    must be always disabled
#endif
    return 0;
}

go in vi and move #if 0 2 lines up to be:

#if 0
int main(int argc, char** argv) {
    int j = 0;
    int i = 0;
//#if 0
    commented out code which
    must be always disabled
//#endif
    return 0;
}
#endif
return to IDE and see unresolved identifiers i and j (they are not in grayed out block) see attachement

-J-Dcnd.modelimpl.trace.external.changes=true shows that we receive external modification and in fact file was reparsed correctly, because no more main function in navigator

External updates: fileChanged BaseFileObj$FileEventImpl[file=/home/vv159170/NetBeansProjects/CppApplication_6/main.cpp,time=Fri May 07 19:51:26 MSD 2010,expected=false]
External updates: scheduling update for MasterFileObject[/home/vv159170/NetBeansProjects/CppApplication_6/main.cpp@1a850c5:1cf4467,valid=true]
External updates: running update task
Updating for MasterFileObject[/home/vv159170/NetBeansProjects/CppApplication_6/main.cpp@1a850c5:1cf4467,valid=true]
=== Starting parser queue stopwatch CppApplication_6
External updates: update task finished
 parsing /home/vv159170/NetBeansProjects/CppApplication_6/main.cpp 55 ms
 === Stopping parser queue stopwatch CppApplication_6: 	 8688 ms
Slowest Files for CppApplication_6 are:
 file=/home/vv159170/NetBeansProjects/CppApplication_6/main.cpp 368 ms