In the following code, libstdc++'s debug mode does not catch the use of a potentially invalidated std::string iterator.

  #define _GLIBCXX_DEBUG
  #define _GLIBCXX_DEBUG_PEDANTIC

  #include <string>
  #include <vector>
  #include <iostream>

  int main()
  {
    typedef std::string S;

    S s (3, 'x');
    S::iterator i = s.begin(); ++i;
    s.push_back('y');
    std::cout << *i << std::endl; // just outputs 'x'
  }

Since the push_back may invalidate i (per 21.3 para 5, 4th item), libstdc++'s debug mode should emit an error and abort.

If I change the typedef to std::vector<char>, then the indicated line /does/ cause libstdc++ to emit an error ("attempt to dereference a singular iterator") and abort.