Initializer_list initialization of std::set

This is how my code looks like

#include <iostream>
#include <set>
using namespace std;

enum Enum_type 
{
    Enum_type_1 = 1,
    Enum_type_2,
    Enum_type_3,
    Enum_type_4
};

class my_class
{
public:

    my_class(Enum_type type) :
        source_type(type)
    {}

    bool operator<(const my_class &another) const;

    Enum_type source_type;
};

bool my_class::operator<(const my_class& another) const
{
    return true;
}

int main()
{
    std::set<my_class> bracers_initialized_set {
        my_class{Enum_type_1},
        my_class{Enum_type_2},
        my_class{Enum_type_3},
        my_class{Enum_type_4}};

    cout<< "bracers_initialized_set.size() " <<  bracers_initialized_set.size() <<endl;
    for (auto my_class_ : bracers_initialized_set) {
        cout << "enum value: " << my_class_.source_type << endl;
    }
    cout<< "bracers_initialized_set.size() " <<  bracers_initialized_set.size() <<endl;

    std::set<my_class> inserted_set;
    if (inserted_set.insert(my_class(Enum_type_1)).second) {
        cout << "inserted_1" << endl;
    }
    if (inserted_set.insert(my_class(Enum_type_2)).second) {
        cout << "inserted_2" << endl;
    }   
    if (inserted_set.insert(my_class(Enum_type_3)).second) {
        cout << "inserted_3" << endl;
    }
    if (inserted_set.insert(my_class(Enum_type_4)).second) {
        cout << "inserted_4" << endl;
    }

    cout<< "inserted_set.size() " <<  inserted_set.size() <<endl;
    for (auto my_class_ : inserted_set) {
        cout << "enum value: " << my_class_.source_type << endl;
    }
    cout<< "inserted_set.size() " <<  inserted_set.size() <<endl;
}

And this is the output:

bracers_initialized_set.size() 4
enum value: 2
enum value: 1
bracers_initialized_set.size() 4
inserted_1
inserted_2
inserted_3
inserted_4
inserted_set.size() 4
enum value: 4
enum value: 3
enum value: 2
enum value: 1
inserted_set.size() 4

As you can see the set initialized with initializer_list behaves bad (size is different than number of iterations). If I implement operator< this way:

bool my_class::operator<(const my_class& another) const
{
    return source_type<another.source_type;
}

then the output is correct for both examples.

However shouldnt the initializer_list initialization and insertion output be the same, regardless of how the operator< looks like? Also shouldnt size always reflect the number of elements?

$ gcc -v

COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.8.4-2ubuntu1~14.04' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04) 

~Marcin