[TYPO3] Extension + url mystery problem

[Frank Sonck]

Hello everyone,

On my testsite (src version 4.1.5) I have this strange URL problem: when 
using several extensions I get a 'page not found' error.

For example when using tx_comments extension on a tt_news article page I 
have this as my url:

http://www.mytestsite.com/index.php?id=306&tx_ttnews[tt_news]
=443&cHash=7fb568c9b5

When submitting my comment under the article I get this url:

http://www.mytestsite.com/index.php?id=306&tx_ttnews[tt_news]
=443&no_cache=1

And this error:

Error!
Reason: The requested page does not exist!

On my live site (src version 4.1.3) this works fine.

1/ It is not a problem of the extension. I also have this with the 
dmmjobcontrol extension for example.

Url of page with jobs:
http://www.mytestsite.com/index.php?id=400
Url to page with detail of a job:
http://www.mytestsite.com/index.php?id=400&tx_dmmjobcontrol_pi1[job_uid]=2
And this gives the same error.

2/ It's not a htaccess problem because replacing my htaccess with the 
default (install) version or the version on my live site doesn't help
3/ Doesn't seem to be a realurl problem because deactivating realurl 
doesn't change anything. When de-installing realurl I don't get the 
"requested page doesn't..." anymore, I just get kicked to the homepage 
(baseurl)
4/ I've upgraded the src to 4.1.5, deleted the temp_CACHED files, 
deinstalled extensions that I installed recently and so on but no 
solution.

If I continue stripping down the site I'll have to restart from scratch I 
fear. So my question is whether someone has experience with this problem 
OR has debugging suggestions as to how to attack this kind of problem?

Thanx a lot and...
Best wishes for 2008 to all of you.

Greetings,
Frank Sonck