I'm using Apache 1.3.17, PHP 4.0.4pl1.
Seems like PHP doesn't like some POST data if they
are send via HTTP/1.0 and HTTP/1.1 in different requests.
The script in question is like this (name: var.php):

<FORM NAME="FORM_POST" ACTION="var.php" METHOD=POST>
Form with POST:<INPUT TYPE=SUBMIT NAME="TEST" VALUE="+???????">
</FORM>

The way to crash PHP:
1) in HTTP/1.0 browser (like Netscape 4.76), click on the submit
   button couple of times,
   enough so that the POST request got to each running httpd
   daemon
2) do HTTP/1.1 request, possibly via telnet, like:

POST /var.php HTTP/1.1
Host: localhost
Content-Length: 1

   at this point, server should wait for the data, but it crashes
   instead. If I look at traceback in gdb, it crashes in _efree()
   (I can provide the exact backtrace if needed).

If the bug is not repeatable for you and would need some more information, feel free to contact me.