DrawThemeBackground() is not painting tab properly - c

Question

When I use DrawThemeBackground() with part TABP_TABITEMRIGHTEDGE and state TIRES_NORMAL it leaves a rect 2 pixels wide on the right unpainted. It doesn't happen with part TABP_TABITEM, TABP_TABITEMLEFTEDGE or TABP_TABITEMBOTHEDGE. What can I do to fix this?
Edit: This only happens in windows 10 and not in widnows xp. I could erase the whole background, then paint the tab and this would solve my problem, and I wouldn't see any flicker in windows 10, but it will flicker in older versions of windows and I don't want that, so I erase the background excluding the area occupied by the tab. In windows 10 it leaves a black rect 2 pixels wide to the right of the tab. Is there a theme function that tells you how much of the rect specified to DrawThemeBackground() will be painted by DrawThemeBackground()?
#include <windows.h>
#include <uxtheme.h>
#include <vsstyle.h>
#include <vssym32.h>
#pragma comment(lib, "uxtheme.lib")
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
static HTHEME hTheme;
static HBRUSH hbrBkg;
switch(msg)
{
case WM_CREATE:
hTheme = OpenThemeData(0, L"Tab");
hbrBkg = CreateSolidBrush(RGB(0, 120, 120));
break;
case WM_PAINT:
{
HDC hdc;
PAINTSTRUCT ps;
hdc = BeginPaint(hwnd, &ps);
if(hdc)
{
HBRUSH hbr = CreateSolidBrush(RGB(255, 0, 0));
if(hbrBkg) FillRect(hdc, &ps.rcPaint, hbrBkg);
if(hbr)
{
RECT rc = { 4, 4, 104, 44 };
FillRect(hdc, &rc, hbr);
if(hTheme) DrawThemeBackground(hTheme, hdc, TABP_TABITEMRIGHTEDGE, TIRES_NORMAL, &rc, 0);
DeleteObject(hbr);
}
EndPaint(hwnd, &ps);
}
}
break;
case WM_DESTROY:
if(hTheme) CloseThemeData(hTheme);
if(hbrBkg) DeleteObject(hbrBkg);
PostQuitMessage(0);
break;
default:
return DefWindowProcW(hwnd, msg, wParam, lParam);
}
return 0;
}
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, int nCmdShow)
{
const WCHAR szClassName[] = L"Themes";
WNDCLASSEXW wc;
HWND hwnd;
MSG msg;
SecureZeroMemory(&wc, sizeof(WNDCLASSEXW));
wc.cbSize = sizeof(WNDCLASSEXW);
wc.hCursor = LoadCursorW(0, IDC_ARROW);
wc.hIcon = LoadIconW(0, IDI_APPLICATION);;
wc.hInstance = hInstance;
wc.lpfnWndProc = WndProc;
wc.lpszClassName = szClassName;
if(!RegisterClassExW(&wc)) return 0;
hwnd = CreateWindowExW(0, szClassName, L"Test", WS_OVERLAPPEDWINDOW, 140, 140, 440, 240, 0, 0, hInstance, 0);
if(!hwnd) return 0;
ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);
while(GetMessageW(&msg, 0, 0, 0) > 0)
{
if(!IsDialogMessageW(hwnd, &msg))
{
TranslateMessage(&msg);
DispatchMessageW(&msg);
}
}
return (int)msg.wParam;
}