a little about MSG Handing about the WM_CHAR

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C++

MFC

static LRESULT CALLBACK ComboBox_Proc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam){
case WM_CHAR:
    if(VK_BACK ==wParam)//让回退正常处理
        return CallWindowProc((WNDPROC)GetProp(hwnd, TEXT("Wprc")), hwnd, msg, wParam, lParam);
    //....

when I purely pressed VK_BACK the if clause will work; wParam is 0x00000008.
But When I pressed VK_BACK with Ctrl-pressed,wParam is 0x0000007f.
I just don't understand it, why the wParam get so? Is some rule here?

In the mean time,If I sometimes need to deal with different Key_Down ,and may with some some Ctrl_Key pressed,Ctrl or Alt or Shift,How Can I deal with it ?

NOTE:
In above sample.GetKeyState() is not applicable!
Becuse the wParam's value changed!