Why the application receives 2 mouse clicks when I send out 1 mouse_event?

Sometimes it seems multiple mouse clicks are received by the application who owns (dx, dy) location while the following code section only executes once:

mouse_event(MOUSEEVENTF_ABSOLUTE | MOUSEEVENTF_MOVE, (DWORD)dx, (DWORD)dy, 0, 0);
mouse_event(MOUSEEVENTF_ABSOLUTE | MOUSEEVENTF_LEFTDOWN, (DWORD)dx, (DWORD)dy, 0, 0);
mouse_event(MOUSEEVENTF_ABSOLUTE | MOUSEEVENTF_LEFTUP, (DWORD)dx, (DWORD)dy, 0, 0);

Can someone explain this? Should I use some other function to avoid it? BTW I can only control the application which sends out the mouse click.

Thank you in advance!

First, what does mouse_event do ? I don't recall anything like it in the API, is it an extension, if so, which ?

Have you tried to only send an up or down message ? Is there maybe a CLICK constant instead of UP or DOWN ?

Did more test and found that the section of code doesn't only execute once when multiple mouse clicks were simulated.

Here is what happened: I use a program to enumerate the windows on the desktop, and when I see some specific window, I will simulate a mouse click to that window. However, sometimes the window can be found during enumeration but it doesn't really "exist" --- means it is not visible and you can't click it. The mouse click will go to the window "behind" the invisible one. That's why I felt like there are more mouse clicks than it should.

This is just a clarification and sorry for the confusion!