[TYPO3-calendar] calendar links are not working

[Hans-Wendel Thul]

Hello folks,

we have problems with the calendar extension at our typo3 site.

If we click on the link "next month" in the month view (showing november 
2011), the page is rendered in a new browser tab (which is not intended) 
showing the same old data (month november instead of december).

The link looks like this:

https://xxx.xxxxxx.xxx/index.php?id=1112&tx_cal_controller[year]=2011&tx_cal_controller[month]=12&cHash=254c3e11629002ff24fb4ad5552acafd

Same happens with all the other next and prev links (in day view e.g.).

No realURL, no simulate static urls installed. Caching framework in 
typo3 is active.

None of the logs (apache, php, developerlog) shows warnings or errors 
concerning the calendar extension.

We stuck in the middle of nowhere. Any help is appreciated.

Calendar extension is version 1.4.1
Typo3 version is 4.5.0 running on Apache/2.2.17 (Win32) DAV/2 
mod_ssl/2.2.17 OpenSSL/0.9.8o PHP/5.3.4 mod_perl/2.0.4 Perl/v5.10.1
PHP version is 5.3.5
Web server OS is Windows 2008 R2

Hans Thul