I tried to edit a template and have it saved to the file system, but always the ACP Gui told me, the file is not writeable. I don't have safe mode on and the permissions are set alright.

I then read through the code and found out that the $safe_mode variable defindes in adm/index.php on line 48 gets always set to TRUE.

$safe_mode = (@ini_get('safe_mode') || @strtolower(ini_get('safe_mode')) == 'on') ? true : false;

ini_get('safe_mode') returns the string 'off' (in my case, which will result in the boolean value TRUE for the string is not empty. TRUE || anything is TRUE.. so $safe_mode will always be true, wether safe_mode is actually on or off.