a design problem about the message WM_PAINT and SetTimer function

(Images are below)I am trying making a tetris game with winapi. I have defined a 10 * 20 RECT array(mapRect[10][20]), which I use to print my map(the map info is stored by a structure called maptrn, only including a 10 * 20 int array). I use setTimer() function to update mapRect for a printing test(), so I add a function called drawMap() (the function is to invalidate all mapRect members) into TimerProc() to invalidate them. But the problem is that after a while the window is redrawn abnormally, and, more exactly, it didn't execute some of the redraw commands, and the style of all the messageboxes are changed. How can I solve the problem?

for(int i = 0; i < HEIGHT; i++) for(int j = 0; j < WIDTH; j++)            InvalidateRect(hwnd, &MapRect[i][j], TRUE);
}

for(int i = 0; i < HEIGHT; i++) for(int j = 0; j < WIDTH; j++)            FillRect(hdc, &MapRect[i][j], CreateSolidBrush(MinoColor[mt.mapTrn[i][j]]));
}

void CALLBACK timerFunc(HWND hwnd, UINT uMsg, UINT_PTR nTimerID, DWORD dwTime)
{
    mino.type = (mino.type + 1) % 8;
    invalidMap(hwnd);
}

...

//In case WM_PAINT:
hdc = BeginPaint(hwnd, &ps);


FillRect(hdc, &MsgRect, CreateSolidBrush(BGCOLOR));

//DrawText(hdc, TEXT("MsgRect Test"), -1, &MsgRect, 0);
//DT_SINGLELINE | DT_CENTER | DT_VCENTER            

RectPrintf(hdc, &MsgRect, TEXT("This is %d"), combine(map, mino).mapTrn[1][1]);


drawMap(combine(newMap, mino), hdc);            
break;

中文：我在用winapi写一个俄罗斯方块游戏。开始我定义了一个mapRect的RECT[10][20]类型的数组，然后我用maptrn（我定义的，包含10 * 20的int数组的结构体）的一个对象来记录地图数据。我还用到了setTimer函数来更新地图的打印测试，所以在计时器proc函数里面加入了drawMap函数（我定义的，将所有mapRect给invalidate掉）。但是问题在于，程序开始一段时间后，他会出现更新上的错误，更准确地说，是某些代码好像没执行，以及messagebox的风格改变了。我应该如何解决？

pic1 normal display

pic2 abnormal display (after the blue text appears in debug console)

pic3 abnormal msgbox(the style and text(original one is "Do you want to quit Tetris?"))

pic4 when this text appears the application doesn't work well as I think