WordPress not writing htaccess (Not a rights problem)

Hi,

after two days of cursing, testing, searching the internet and reading tons of tutorials I decided to post my problem here. From the start on WordPress wasn’t writing to the .htaccess file. It doesn’t create a debug file either.
First I created my own .htaccess file with the needed rules for permalinks. After I started to use W3 Total Cache this became to complicated. I would love to see wordpress creating the nescessary rules by it’s own. So I started to debug.

– The file rights:
The standard file rights are 644 in my hosting package. The user is the user php is running under. Of course I tried rights like 666. It did’nt change anything.

– Testing PHPs ability to create and write files:
I wrote a small script to test whether PHP is capable to write a file.

$testfile = fopen("testfile","w");
fwrite($fp,"Test");
fclose($fp);

Everything works fine. The created file has the right 644.

– Testing a plugin to write to the .htaccess File
I installed WP Htaccess Editor to test whether it’s possible to write to the file with it. It is. Not a problem. But wordpress is still not writing rewrite rules to .htaccess.

Testing whether a plugin or theme blocks the writing
I deactivated all plugins and changed the theme (Thememakers Almera) to test whether one of them causes the problem. Nope, WordPress is still not writing anything to the .htaccess file.

Is WordPress writing to a wrong file?
I searched my virtual host for another .htaccess in another directory. There is one, but WordPress isn’t writing to it either.

I activated the debugging and debug log in wp-config, but WordPress isn’t creating a log file or producing any errors. That’s the most astonishing thing. I don’t get any error messages when I try to change the permalink settings. Everything appears to be fine but nothing is written to the file. When I remove the write rights from it (444) WordPress complains about that… So I’m definetly looking for the right file.

Well, I’m running out of ideas what else to test. Does anybody have an idea? Or better, did someone run into the same problem and solved it? I’m not very eager to go into the source code of wordpress…

The server is an Apache 2.x with PHP 5.4.17

Hope someone can help! Thank you in advance! ??