Proxy chaining dns error when requesting php-page

Hi,
I am trying to use an internal-external proxy setup where all non
intranet requests should be forwarded to the external cache-parent
(proxy chaining). This works for "normal" URL's but on all pages where
(php-)data is send in the <fqdn>.php?<whatever> way I get an dns
error(domain name does not exist). When stripping of the dynamic part
(?<whatever>) I get the page without any problem.
The logs mention "first-up-parent/<parent-name>" for successfully
served pages and "none/-" for the dns-error pages. I assume squid does
not send the request to the parent seen the log-entry ("none/-") which
might explains the dns-error (only the parent proxy has access to
external dns). I wonder why the php-pages do not get handled properly
when data is send.

I have the following parent config line:
"cache_peer <parent-proxy> parent <parent-proxy-port> 0 no-query
no-digest login=PASS"
I am running squid/2.5stable-nt.

Does anyone have a clue how to get this working?

Thanks,
Ron