Why does CreateFile modify my ShareMode parameter?

In Windows I am opening a file with CreateFile. I want to open the file with much privileges (in dwDesiredAccess parameter) and share only a subset of them (in dwShareMode parameter).

#include <iostream>
#include <Windows.h>

int main()
{
	const WCHAR* wszFile = LR"(D:\temp\myfile.txt)";
	HANDLE hFile1 = CreateFileW(wszFile, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile1 == INVALID_HANDLE_VALUE)
		std::cout << "File 1 opening failed with error code " << GetLastError() << std::endl;
	else
		std::cout << "File 1 opening succeeded." << std::endl;

	HANDLE hFile2 = CreateFileW(wszFile, GENERIC_READ, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile2 == INVALID_HANDLE_VALUE)
		std::cout << "File 2 opening failed with error code " << GetLastError() << std::endl;
	else
		std::cout << "File 2 opening succeeded." << std::endl;

	HANDLE hFile3 = CreateFileW(wszFile, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile3 == INVALID_HANDLE_VALUE)
    	std::cout << "File 3 opening failed with error code " << GetLastError() << std::endl;
	else
    	std::cout << "File 3 opening succeeded." << std::endl;

	CloseHandle(hFile1);
	CloseHandle(hFile2);
	CloseHandle(hFile3);

	return 0;
}

I would expect that the first two calls succeed and the third call fails, but instead the first and the third call succeed and the second call fails.
This means that CreateFile did modify my dwShareMode parameter flags.

Why does this happen?

I tried some more times and found an explaination. I extended my previous code by two more calls.

#include <iostream>
#include <Windows.h>

int main()
{
	const WCHAR* wszFile = LR"(D:\temp\myfile.txt)";
	HANDLE hFile1 = CreateFileW(wszFile, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile1 == INVALID_HANDLE_VALUE)
		std::cout << "File 1 opening failed with error code " << GetLastError() << std::endl;
	else
		std::cout << "File 1 opening succeeded." << std::endl;

	HANDLE hFile2 = CreateFileW(wszFile, GENERIC_READ, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile2 == INVALID_HANDLE_VALUE)
		std::cout << "File 2 opening failed with error code " << GetLastError() << std::endl;
	else
		std::cout << "File 2 opening succeeded." << std::endl;

	HANDLE hFile3 = CreateFileW(wszFile, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile3 == INVALID_HANDLE_VALUE)
		std::cout << "File 3 opening failed with error code " << GetLastError() << std::endl;
	else
		std::cout << "File 3 opening succeeded." << std::endl;

	HANDLE hFile4 = CreateFileW(wszFile, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile4 == INVALID_HANDLE_VALUE)
		std::cout << "File 4 opening failed with error code " << GetLastError() << std::endl;
	else
		std::cout << "File 4 opening succeeded." << std::endl;

	HANDLE hFile5 = CreateFileW(wszFile, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
	if(hFile5 == INVALID_HANDLE_VALUE)
		std::cout << "File 5 opening failed with error code " << GetLastError() << std::endl;
	else
		std::cout << "File 5 opening succeeded." << std::endl;

	CloseHandle(hFile1);
	CloseHandle(hFile2);
	CloseHandle(hFile3);
	CloseHandle(hFile4);
	CloseHandle(hFile5);

	return 0;
}

The fourth call also fails. So there is the proof that the ShareMode parameter hasn't been modified by CreateFile.
The fifth call succeeds, although it grants an additional share mode (FILE_SHARE_DELETE) which is not available due to previous calls.
My problem is that the meaning of ShareMode is ambiguous depending on whether the file is opened for the first time or for subsequent times:

• In the first time you specify the share mode for all subsequent file access. The following CreateFile calls may not specify more privileges than this in their dwDesiredAccess parameter.
• Starting with the second time you must specify the same share mode given in the first call plus the share mode required to allow the dwDesiredAccess parameter of the previous calls. But you are allowed to share more (although there will not be shared more (as long as the other handles are open...?)).

My problem was that I expected that dwShareMode only needs to know the dwShareMode parameter of the previous calls and not that it must also know the required access rights for previous dwDesiredAccess parameters.

Unfortunately this isn't clearly described in the MSDN. I had already read the following article, which says:

https://learn.microsoft.com/en-us/windows/win32/fileio/creating-and-opening-files

> An application also uses CreateFile to specify whether it wants to share the file for reading, writing, both, or neither. This is known as the sharing mode. An open file that is not shared (dwShareMode set to zero) cannot be opened again, either by the application that opened it or by another application, until its handle has been closed. This is also referred to as exclusive access.
>
> When a process uses CreateFile to attempt to open a file that has already been opened in a sharing mode (dwShareMode set to a valid nonzero value), the system compares the requested access and sharing modes to those specified when the file was opened. If you specify an access or sharing mode that conflicts with the modes specified in the previous call, CreateFile fails.

The behavior of dwShareMode makes sence, but isn't fully described there.