TB_SETPADDING message has no effect on vertical padding

I an trying to set the toolbar padding to zero, but the TB_SETPADDING message effect only to the horizontal padding, but not to the vertical padding.

I set the color scheme to red and green, to highlight the button border, and this is the output:

can someone explain me why is this happening?

this is the full code:

#include <windows.h> 
#include <stdlib.h>
#include <CommCtrl.h>
#pragma comment(lib, "comctl32.lib")

#define IDB_PRINT 40000

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
HINSTANCE instance;

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    instance = hInstance;

    WNDCLASSEX wcex; 

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style           = CS_HREDRAW | CS_VREDRAW; 
    wcex.lpfnWndProc    = WndProc; 
    wcex.cbClsExtra     = 0; 
    wcex.cbWndExtra     = 0;  
    wcex.hInstance      = hInstance;
    wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_APPLICATION));  
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW); 
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1); 
    wcex.lpszMenuName   = NULL; 
    wcex.lpszClassName  = L"Example"; 
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_APPLICATION));

    RegisterClassEx(&wcex);

    HWND hWnd = CreateWindow(L"Example", L"", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
        500, 500, NULL, NULL, hInstance, NULL);

    // Initialize common controls.
    INITCOMMONCONTROLSEX icex;
    icex.dwSize = sizeof(INITCOMMONCONTROLSEX);
    icex.dwICC   = ICC_COOL_CLASSES | ICC_BAR_CLASSES;
    InitCommonControlsEx(&icex);

    // create toolbar
    HWND hToolbar = CreateWindowExW(WS_EX_TOOLWINDOW | TBSTYLE_EX_HIDECLIPPEDBUTTONS, TOOLBARCLASSNAME, NULL, CCS_NODIVIDER | WS_CHILD | WS_VISIBLE | CCS_ADJUSTABLE | TBSTYLE_ALTDRAG | TBSTYLE_FLAT | TBSTYLE_TOOLTIPS,
        0, 0, 0, 0, hWnd, (HMENU)0, instance, NULL);

    SendMessage(hToolbar, TB_SETMAXTEXTROWS, 0, 0);

    // create image list
    HIMAGELIST hImageList = ImageList_Create(20,20, ILC_COLORDDB, 4, 0);
    ImageList_Add(hImageList, LoadBitmap(instance, MAKEINTRESOURCEW(IDB_PRINT)), NULL);
    ImageList_Add(hImageList, LoadBitmap(instance, MAKEINTRESOURCEW(IDB_PRINT)), NULL);

    // set the image list
    SendMessage(hToolbar, TB_SETIMAGELIST, (WPARAM)0, (LPARAM)hImageList);
    SendMessage(hToolbar, TB_BUTTONSTRUCTSIZE, (WPARAM)sizeof(TBBUTTON), 0);

    // create button
    TBBUTTON tbb[1] = 
    { 
        {0, 0, TBSTATE_ENABLED, BTNS_AUTOSIZE, {0}, 0, (INT_PTR)L"Print"},
    };

    // add button to the toolbar
    SendMessage(hToolbar, (UINT)TB_ADDBUTTONS, 1, (LPARAM)&tbb);
    SendMessage(hToolbar, TB_SETBUTTONSIZE, 0, MAKELPARAM(20, 20));
    SendMessage(hToolbar, TB_AUTOSIZE, 0, 0);
    DWORD res = SendMessage(hToolbar, TB_SETPADDING, 0, MAKELPARAM(0, 0));

    // set color scheme to red and green
    COLORSCHEME cs;
    cs.dwSize = sizeof(cs);
    cs.clrBtnShadow = RGB(255, 0, 0);
    cs.clrBtnHighlight = RGB(0, 255, 0);
    SendMessage(hToolbar, TB_SETCOLORSCHEME, 0, (LPARAM)&cs);

    // set the padding size to zero
    SendMessage(hToolbar, TB_SETPADDING, 0, MAKELPARAM(0, 0));

    // show the toolbar
    ShowWindow(hToolbar, SW_SHOW);

    // show the main window
    ShowWindow(hWnd, nCmdShow);

    MSG msg;

    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);  
        DispatchMessage(&msg); 
    }

    return (int) msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
        case WM_CREATE: 
            return 0;

        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
    }
}

=== EDIT ===

this what I have in my resource file:

#define IDB_PRINT 40000
IDB_PRINT BITMAP "print.bmp"

and this is the print.bmp file: