PostMessage WM_KEYDOWN while holding CTRL?

If i be holding the CTRL key down while sending a PostMessage containing WM_KEYDOWN it 'mess' with the message.

I couldn't understand what really happens, if it sends CTRL plus the message being sent or what?

How to reproduce:

Launch notepad and hold the CTRL key while the code is running

#include <windows.h>
#include <iostream>

struct extraKeyInfo
{
    unsigned short repeatCount;
    unsigned char scanCode;
    bool extendedKey, prevKeyState, transitionState;

    operator unsigned int()
    {
        return repeatCount | (scanCode << 16) | (extendedKey << 24) |
            (prevKeyState << 30) | (transitionState << 31);
    }
};


int _tmain(int argc, _TCHAR* argv[])
{

    auto hwnd = FindWindow(0, L"Untitled - Notepad");
    HWND hEdit = FindWindowEx(hwnd, NULL, TEXT("Edit"), NULL);

    for (char ch = 'a'; ch <= 'z'; ch++) // Output a-z in Notepad
    {
        short vkCode = LOBYTE(VkKeyScan(ch));

        extraKeyInfo lParam = {};
        lParam.scanCode = MapVirtualKey(vkCode, MAPVK_VK_TO_VSC);

        PostMessage(hEdit, WM_KEYDOWN, vkCode, lParam);

        lParam.repeatCount = 1;
        lParam.prevKeyState = true;
        lParam.transitionState = true;

        PostMessage(hEdit, WM_KEYUP, vkCode, lParam);
        Sleep(200);
    }

}

Is possible somehow to send just the desired key into the PostMessage independent if i have any keydown?