c++静态变量和静态对象

#include
using namespace std;
class A
{
static int inc;
static int count;
int id;
public:
A()
{
count++;
id = inc++;
cout << "id = " << id << ", count = " << count << endl;
}
~A() { count--; }
};
int A::inc = 0;
int A::count = 0;
static A a;

int main()
{
A a;
{
A a;
}
A b;
return 0;
}
id = 0, count = 1
id = 1, count = 2
id = 2, count = 3
id = 3, count = 3
为何第三次后count的量就不变了

第二个a调用了析构