I don't see a bug in PHP here.  The problem is your code, since
you first modify the file(s), and then execute pathmonitor.exe
which waits possibly indefinitely for modifications.
Additionally, you should not pass the name of a file to
pathmonitor.exe, but rather its directory:

    shell_exec("pathmonitor.exe " . dirname($_GET['path']));

"The problem is your code, since
you first modify the file(s), and then execute pathmonitor.exe
which waits possibly indefinitely for modifications"

This is not true.
test1, test2 and test3.html, they all make a request onload to insert.php which starts pathmonitor.exe. At this point pathmonitor.exe is waiting for something to happen.

Then after that use "write-buttons.html" to write in the folders.  

This is what the program should do, no matter which buttons you press, two folders gets a write (One folder is one of the options in "write-buttons.html", the other folder is folder1). When the write happens the ajax request is returned and new request is sent back to start a new wait.

It works in the beginning, but then after some "button pressing", one of the two ajax requests that should return doesn't return.



So I still belive it's a bugg, don't you think?

I wrote wrong at the beginning of my last comment. This is how it should be instead:

test1, test2 and test3.html, they all make a request onload to monitor.php (NOT to insert.php)