Works absolutely fine on my very standard, almost vanilla installation.

Code:

  #include <vector>
  using namespace std;
  int main()
  {
    vector<int> beans;
    beans.resize(5);
    beans[3] = 4;
    beans [4] = 66;
  }

Build command:

  g++ -g 156.cpp

gdb debugging session:

  GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
  SKIPPED OUT WARRANT INFO HERE
  Reading symbols from /badcode/a.out...done.
  (gdb) break 156.cpp:10
  Breakpoint 1 at 0x4008e6: file 156.cpp, line 10.
  (gdb) run
  Starting program: /badcode/a.out

  Breakpoint 1, main () at 156.cpp:10
  10	  beans [4] = 66;
  (gdb) print beans[3]
  $2 = (int &) @0x60401c: 4
  (gdb) print beans[4]
  $3 = (int &) @0x604020: 0