php-cgi processes not closed off after script finishes executing - PHP5.3.3, Win Server 2003, apache

Question

I have a strange problem running PHP5.3.3 on a Windows 2003 server with Apache.

Sometimes scripts that have been initiated finish the work that they are doing, but the process does not close.

This can leave a large number of orphan php-cgi.exe processes running, but not, apparently, doing anything (not using any CPU time).

After a while, these build up and cause performance issues on the server.

There doesn't seem to be a fault with the PHP script itself, as normally it runs and closes fine, it's just somethings it doesn't, and there doesn't seem to be any obvious pattern about it either.

Also, we didn't have this problem before moving from PHP4 to PHP5.3.

Any ideas? It feels like some config I've got wrong in Apache or PHP somewhere? I am NOT using the apache dll to run PHP,and neither is this an option for me.

thanks in advance