system.connect intermittently returns response without session id

I am using AMFPHP and Services modules to interact with Flash. I am having an intermittent problem when executing system.connect: When it's working properly it returns a response like this:

HTTP/1.1 200 OK
Date: Thu, 10 Sep 2009 15:20:29 GMT
Server: Apache
Expires: Thu, 10 Sep 2009 19:20:29 GMT
Last-Modified: Thu, 10 Sep 2009 15:20:29 GMT
Cache-Control: no-store
Pragma: no-store
Content-length: 291
Keep-Alive: timeout=15, max=83
Connection: Keep-Alive
Content-Type: application/x-amf

????AppendToGatewayUrl????I?F?SESS9e6947a6cfb27634029d183eeb11f96a=ba5061a12a72f4483935e8c7212c62fb??
/1/onResult?null?????sessid? ba5061a12a72f4483935e8c7212c62fb?user?userid??????????hostname?10.224.224.159?roles????1?anonymous user?? ?session???cache??????????? ??

When it fails it returns this (no session ID):

HTTP/1.1 200 OK
Date: Thu, 10 Sep 2009 08:19:36 GMT
Server: Apache
Expires: Thu, 10 Sep 2009 01:19:36 GMT
Last-Modified: Thu, 10 Sep 2009 08:19:36 GMT
Cache-Control: no-store
Pragma: no-store
Content-length: 129
Keep-Alive: timeout=15, max=84
Connection: Keep-Alive
Content-Type: application/x-amf

????AppendToGatewayUrl????I?F?SESS3e923b281653185b85089c59e79637ef=963fc4f1ed2f0154fa423a46b661c771??
/1/onResult?null????

It doesn't seem to matter whether I am logged in or not, and I can't find any pattern, it works sometimes, and not others.

I know that I can use an alternate method of getting the session id into the flash but this has worked perfectly except that sometimes it doesn't return the full response.

When I run the services browser it works every time, so not sure if this could be related to AMFPHP since the requests go through there first.

Thanks,

-Aaron