Anaconda: Only STDERR are logged into a file when using %post --log-file in Red Hat Enterprise Linux 6 or %post --log-file seems corrupted after installation

Issue

• I'd like to keep logging of all what's done in the kickstart %post install script.
• All is logged well unless something is printed on standard error. Otherwise, whole previous output is lost and log is starting from this first message printed on stderr.
• I don't want to redirect all commands with 2>&1.