If "FILE1" is a posted file and it is zero bytes in length, the following code will die with a "Failed - none" message:

$tmpfile = $HTTP_POST_FILES["FILE1"]["tmp_name"];
if (!is_uploaded_file($tmpfile)) {
	die ("Failed - " . $tmpfile);
}

Not only does it fail, it leaves a zero-byte "php" temporary file behind in /tmp.

But if the file is non-zero in length, it does not fail, and the temporary file is automatically deleted at exit.

I can reproduce this with IE 4.01sp1, IE 5.5, and Netscape 4.75. My HTML which calls the upload script looks like this:

<form method="POST" action="/doupload.php" ENCTYPE="multipart/form-data">
<input type=file name="FILE1" size=60>
<input type=submit value="Upload File">
</form>