weird issue with PostConstruct in parent class - spring

Question

I have such a simple example:
public class Base<T> {
private String value;
public Base(String value) {
this.value = value;
}
#PostConstruct
private void init() {
System.out.println(value);
}
}
public class StringTest extends Base<String> {
public StringTest(String value) {
super(value);
}
}
public class IntegerTest extends Base<Integer> {
public IntegerTest(String value) {
super(value);
}
}
#Configuration
public class Configuration {
#bean(name="stringtest1")
public Base<?> getStringTest1() {
return new StringTest("string test 1");
}
#bean(name="stringtest2")
public Base<?> getStringTest2() {
return new StringTest("string test 2");
}
#bean(name="integertest1")
public Base<?> getIntegerTest1() {
return new IntegerTest("integer test 1");
}
#bean(name="integertest2")
public Base<?> getIntegerTest2() {
return new IntegerTest("integer test 2");
}
}
The output is
string test 1
string test 2
PostConstruct is only invoked for beans stringtest1 and stringtest2 but not for integertest1 and integertest2.
If I change the configuration to below (change ? to the concrete type)
#bean(name="stringtest1")
public Base<String> getStringTest1() {
return new StringTest("string test 1");
}
#bean(name="stringtest2")
public Base<String> getStringTest2() {
return new StringTest("string test 2");
}
#bean(name="integertest1")
public Base<Integer> getIntegerTest1() {
return new IntegerTest("integer test 1");
}
#bean(name="integertest2")
public Base<Integer> getIntegerTest2() {
return new IntegerTest("integer test 2");
}
I will get the expected output:
string test 1
string test 2
integer test 1
integer test 2
Any idea why my previous code only have the PostConstruct invoked for the first 2 beans?