writing to a file in the include path will give undefined results and is a potential security risk.

As such we do not support it, and you might find that attempting to use fopen() in this way will raise a warning in PHP 5.

I know this very well and I use the function in this example only for own testings which are not official assignable. When it is so risky that way you mean, why is the parameter [in include path] supported for this function? And more, why does it work in 4.3.0 and not in 4.3.2 ?

#1) The path you are attempting to write does not (probably anyway) exist.  Here's why:

You pass: "mail/localmail/105455483215927000_test@test.de.txt" to fopen and tell it to write in the include path.

The include path includes, among other locations: /www/casyincs/mail/localmail 

Adding the includepath to the file requested gives:

/www/casyincs/mail/localmail/mail/localmail/105455483215927000_test@test.de.txt

Notice how the file provided to fopen is seen as a relative path to the include path.  So of course it can't write to the file, the directory /www/casyincs/mail/localmail/mail/localmail doesn't exist.  None of the other path locations leads to a legitimate location either so the write fails.

#2) For boolean options, try to use TRUE rather than merely a value which evaluates to true.

#3) Using the include path with a write is supported because there could be legitimate uses for it (though essoteric ones).  It is however, discouraged because it becomes very easy for the unwary programmer to create a situation wherein system files are overwritten because one of the included paths matches the path passed to fopen and consequently system files are overwritten.  Now, imagine a malicious user finding such a vulnerability in your code, he submits data which results in a PEAR class being overwritten with code which, in turn, compromises the integrity of your system as a whole.

In general, because you already know the path where you want to create your file, using the include_path option only serves to expose you to unpredictable behavior (as you've already seen) without adding to your functionality.

That said, your script probably worked earlier, not because of the version, but because you had '.' (current directory)included in your path.

Thanx for your fast answer.
#1) Include path is www/casyincs, not more. I
pass fopen() the path "mail/localmail/file" so that
the files must be written into the dir:
www/casyincs/mail/localmail/file

I have nothing changed in this script before updating to 4.3.2 so i am wondering what my fault will be.
You are defenitly right regarding the insecurity with writing within the include path, no question.
Nevertheless, what has changed in the new version now regarding this item? (Sorry, but I do not understand what my fault is, and sorry for my english :-) )