check for deleted map entry -> crash ?

I'm using an STL map in my code.
My application sometimes tries to delete things twice from the map.
This leads to a crash in my current code. The problem is probably the
way I check whether it is necessary to delete something (line 44 and 52
in below code).
In the below code the problem is demonstrated, line 65 will cause a
segmentation fault.

     1 #include <iostream>
     2 #include <cstdlib>
     3 #include <map>
     4
     5 using namespace std;
     6
     7 class MyClass
     8 {
     9 public:
    10 MyClass(int);
    11 ~MyClass();
    12 void show();
    13 private:
    14 int nr_;
    15 };
    16
    17 MyClass::MyClass(int nr) : nr_(nr)
    18 {
    19 cout << "MyClass: " << nr_ << " constructed" << endl;
    20 }
    21
    22 MyClass::~MyClass()
    23 {
    24 cout << "MyClass: " << nr_ << " destructed" << endl;
    25 }
    26
    27 void MyClass::show()
    28 {
    29 cout << "Show this MyClass: " << nr_ << endl;
    30 }
    31
    32 typedef map<int, MyClass *> RtdmCyclicTimerMap;
    33
    34 int main(void)
    35 {
    36 RtdmCyclicTimerMap cyclicRtdmTimer_;
    37 map<int, MyClass *>::const_iterator cyclicRtdmIt;
    38
    39 // create 1 & 2
    40 cyclicRtdmTimer_[1] = new MyClass(11);
    41 cyclicRtdmTimer_[2] = new MyClass(22);
    42
    43 // delete 2
    44 if (cyclicRtdmTimer_[2]) {
    45 delete cyclicRtdmTimer_[2];
    46 cyclicRtdmTimer_.erase(2);
    47 } else {
    48 cout << "delete 2 failed" << endl;
    49 }
    50
    51 // delete 2 AGAIN
    52 if (cyclicRtdmTimer_[2]) {
    53 delete cyclicRtdmTimer_[2];
    54 cyclicRtdmTimer_.erase(2);
    55 } else {
    56 cout << "delete 2[2] failed" << endl;
    57 }
    58
    59 // show map -> NOW IT WILL CRASH
    60 cout << endl << "going to show map entries" << endl;
    61 for
(cyclicRtdmIt=cyclicRtdmTimer_.begin();cyclicRtdmIt!=cyclicRtdmTimer_.end();
++cyclicRtdmIt) {
    62 int tKey = cyclicRtdmIt->first;
    63 MyClass *mcPtr = cyclicRtdmIt->second;
    64 cout << "map entry found: key=" << tKey << ", valP=" <<
mcPtr << ", val=";
    65 mcPtr->show();
    66 }
    67 }
    68

This is because line 52 somehow increases the internal map size from 1
to 2 entries.
Isn't it allowed to refer to deleted entries ?
Must it be done with an iterator ?