How to define this tooltip kind

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C++

Windows

WinAPI

I've used this article (http://msdn.microsoft.com/en-us/library/windows/desktop/hh298369%28v=vs.85%29.aspx[^]) to add a tooltip for two regions.

Firstly, I graphically draw two regions:

//first rectangle
HBRUSH brush1 = CreateSolidBrush(RGB(225, 0, 0));
RECT a = {20, 20, 70, 50};
FillRect(GetDC(hwnd), &a, brush1);

//second rectangle
HBRUSH brush2 = CreateSolidBrush(RGB(0, 0, 255));
RECT b = {70, 20, 120, 50};
FillRect(GetDC(hwnd), &b, brush2);

And now I'm trying to add two tips for these two regions:

INITCOMMONCONTROLSEX icc;
InitCommonControlsEx(&icc);
icc.dwSize = sizeof(INITCOMMONCONTROLSEX);
icc.dwICC = ICC_BAR_CLASSES;

HWND tooltip_hwnd = CreateWindowEx(WS_EX_TOPMOST, TOOLTIPS_CLASS, "TooltipIM", WS_POPUP |  TS_NOPREFIX | TTS_ALWAYSTIP, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, hwnd, NULL, (HINSTANCE)GetModuleHandle(NULL), NULL);
     
SetWindowPos(tooltip_hwnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOACTIVATE);
SendMessage(tooltip_hwnd, TTM_SETMAXTIPWIDTH, 0, 200);
SendMessage(tooltip_hwnd, TTM_SETDELAYTIME, TTDT_AUTOPOP, 15000);

TOOLINFO ti = {0};
ti.cbSize = sizeof(TOOLINFO);
ti.uFlags = TTF_SUBCLASS;
ti.hwnd = hwnd;
ti.hinst = (HINSTANCE)GetModuleHandle(NULL);
ti.uId = 1;
ti.lpszText = "first";
RECT frst = {20, 20, 70, 50};
ti.rect.left = frst.left;
ti.rect.top = frst.top;
ti.rect.right = frst.right;
ti.rect.bottom = frst.bottom;
//add tip for first region
SendMessage(tooltip_hwnd, TTM_ADDTOOL, 0, (LPARAM)(LPTOOLINFO)&ti);

ti.uId = 2;
ti.lpszText = "second";
RECT scnd = {70, 20, 120, 50};
ti.rect.left = scnd.left;
ti.rect.top = scnd.top;
ti.rect.right = scnd.right;
ti.rect.bottom = scnd.bottom;
//add tip for second region
SendMessage(tooltip_hwnd, TTM_ADDTOOL, 0, (LPARAM)(LPTOOLINFO)&ti);

And it works fine! But I don't understand why the following happens: when the mouse cursor moves from the first region to the second one, the tooltip window is blinking when changing tips.
https://www.youtube.com/watch?v=cblAF7hUPOA[^]
Why does this happening?
I made an experiment in c++ builder. I put on the form two buttons and placed them next to each other. And the result was next: when the mouse cursor moves from the first button to the second one, the tooltip window does not blink:
https://www.youtube.com/watch?v=ITdYX6bXMUg[^]
How to achieve the same effect in my code?